Eli Whitney Museum

The buildings of the Whitney Armory on the west side of the Mill River were devoted to the machining, finishing, and assembling of parts. In these buildings the Armory workmen made the barrels, drilled, filed and milled the other metal parts to final shape, polished, browned, or blued them, and prepared the wooden stocks for receiving them. Then the whole guns — "lock, stock, and barrel" — were assembled, inspected, and packed in wooden boxes for shipping.

The west bank structures that Eli Whitney, Sr. built for these purposes before his death in 1825 were totally replaced by Eli Whitney, Jr. before his retirement in 1888. The use of machines and the specialization of labor begun by Whitney, Sr. after 1798 were extended by Whitney, Jr., and the workforce of 40 to 60 expanded to 200 or more. To accommodate these changes during the later years of the Armory, the two large buildings in the area west of the river and north of the footbridge that are visible on the 1825 map have given way to the five large buildings on the 1879 map.

Eli Whitney's Armory C. 1825

Eli Whitney's Armory C. 1879

(A) low dam, (B) machine and filing shop, (C) gunstocking shop, (D) (possible) triphammer shop, (E) forging shop, (K) "1860 building", metal-working machinery, (L) "dam building", barrel-making and stocking, (M) milling and turning, (N) steam engine, (O) browning gunbarrels, making boxes, storing patterns, (P) finishing and assembling.

What went on inside the two large buildings of the early Armory? Very little is known in detail about the machinery used at the Armory during the period of its founder, from 1798 to 1825. Eli Whitney himself did not patent or otherwise write descriptions of his machinery, and although his manufactory became something of a tourist attraction, what visitors wrote about it is more enthusiastic than specific. As for direct material evidence, there were no patent models made, and none of the actual machines has survived the 160 years from that period to today.⁴ It is, generally speaking, rare that old and therefore obsolete factory machines escape being scrapped before they are recognized as having historic interest. An indirect type of material evidence about the machinery has survived in museums and private collections, however, namely some of the nearly 35,000 muskets that were produced at the Armory before 1825. The art of interpreting tooling marks on gun parts, in order to infer their process of manufacture, has made a promising start.

When Whitney first asked for a contract to make muskets for the United States, he wrote:⁵

"I am persuaded that Machinery moved by water adapted to this Business would greatly diminish the labor and facilitate the Manufacture of the Article. Machines for forging, rolling, floating, [a kind of filing] boreing, Grinding, Polishing, etc. may all be made use of to advantage."

This gives some indication of what his plans were for machinery, but not necessarily what he put into operation. Three years later, however, his ten-year-old nephew Philos Blake wrote that his uncles factory did contain

"a driling machine and a boureing machine to hour berels and a screw machine and too great large buildings, one nothershop and a stocking shop to stocking guns in, a blacksmith shop, and a trip hammer shop and 500 guns done."⁶

And upon visiting the Whitney Armory two years later, Yale College President Timothy Dwight notes:⁷

"machinery, moved by water, and remarkably adapted in every instance to the purpose in view, is employed for hammering, cutting, turning, perforating, grinding, polishing, etc. etc."

The next eyewitness account we have of the equipment at the Whitney Armory is over twenty years later: the probate inventory that was made of Whitney's property after his death in January 1825.⁸ (See Table I.) Since it is simply a listing of items and their value, it does not distinguish clearly between equipment in use and equipment in storage. But since it is a very long list and includes such trifles as vest and coat buttons and "⁹ bunches fine Brass wire" for 40 cents, it can be assumed to be complete. Among the items located "In the Machine & Filing shop" at the Armory and on the floor below it, were a number of metal-working machines that were probably water-powered, ranging in value from 22 to 400 dollars. For woodworking, however, the Armory seems not to have been mechanized, even though Whitney had earlier alluded to "a machine for boring wood of my own invention."9 By contrast to the metal-working machines listed in the inventory, the items of apparatus for woodworking in the stocking shop were apparently not water-powered, for some are equipped with cranks and all are of much lower value apiece than those in the other building. His gunstock-ers apparently continued to use hand tools to cut the recesses for metal parts into "thoroughly seasoned" gun stocks that were delivered to the Armory from the U.S. government stores, instead of making them with the irregular turning lathe and other gunstocking machines that Thomas Blanchard had invented and were in use at Springfield Armory during the last few years of Whitney's life.¹⁰

Table I Machines and Tools for Working Metal and Wood, Listed in Eli Whitney's Probate Inventory, 1825.
Location Item Value
(in dollars)
Machine & Filing Shop lathe & tools appurtenant 25.00
Milling tools & nitching Machine 75.00
Drilling Machine caps & appurtenances 400.00
Shears & appurtenances - old 150.00
Do [ditto] large cast iron 200.00
Screw Machine & apparatus 100.00
Stamping Do & tools 60.00
Machine for Polishing barrels 22.00
Polishing mac bine & Wheels 75.00

Lower floor of Same Building 1 Grindstone Shaft & Box 85.00
2 Small Do & pullies 14.00

Machine tools for fine boring 18.00
Trip hammers & irons 25.00

Stocking Shop Large Shaving knife .50
Brace & 50 bits 7.00
16 Augers different sizes 6.00
30 Bench & Moulding Tools 20.00
12 Gouges & Chisels sizes .75
1 Framed Compass Saw .75
1 Auger for boring logs 6.00
Machine for twisting [metal] wipers 1.50
4 Sets Tools for stocking with benches and stands 40.00
i turning wheel 8c Crank 5.00
Lathe & whipsaw & broken frame 5.00

The probate inventory, then, suggests that Eli Whitney, Sr. did have water-powered metalworking machines — trip hammers, drills, shears, lathes for turning and boring, machines for making screws, and machines for grinding and polishing, but no water-powered woodworking machines.

Some daybooks of the early Armory have survived and give clues as to the work processes going on, but are not explicit as to which of them were mechanized. For instance, Eli Whitney paid $114.75 to Phineas Tyler, one of his workers, for filing 459 locks between September 6, 1809 and April 19, 1810, at 25 cents each.¹¹ Apparently such filing was unmechanized, instead of being performed by the machine for "floating" that Whitney's letter to Wolcott in 1798 had envisioned. This can be inferred not only from the absence of any eyewitness report of such a machine, but also by the presence, elsewhere in the 1825 inventory, of some four hundred hand files of 24 different varieties. It has been argued that so many files would be unnecessary in a factory equipped with a machine for filing.¹² (Some perspective on this number may be useful: in Springfield Armory in 1809, to complete 100 muskets required using up 104 files, 60 of which were for the lock filing, 6 for stocking.¹³ At that rate, the files on hand at the Whitney Armory when the inventory was taken in 1825 would be not quite enough for one lot of 500 guns.)

Close inspection of tooling marks on lockparts from Whitney Armory muskets made before 1825 confirms the written clues about hand-filing instead of machining for flat and irregularly curved surfaces. But it also reveals machining for cylindrical shapes, such as screw shanks and tumbler pivots. Such marks have been interpreted to mean that Eli Whitney was using a water-powered hollow mill, perhaps identifiable as either "the screw machine" mentioned by Philos in 1801 and the inventory in 1825, or as the "milling tools" associated with the "nitching machine" in the inventory.¹⁴ The slots in the heads of the screws used in these muskets show that they were cut by a circular saw, probably in the "nitching machine". Machine tool historian Edwin Battison has concluded, from the dates of the Whitney muskets he examined, that "there is evidence for moving back the date for the introduction of two specialized types of milling [the circular saw and the hollow mill] in the [American] arms industry to sometime between 1803 and 1809."¹⁵

Perhaps more important for Eli Whitney's new manufactory than his water-powered machines were his methods of organizing the work to be performed by hand as well as by machine. Rather than attempt to employ already experienced gunsmiths, who were scarce, Whitney organized the work of making a musket so that it could be performed by workmen with no particular gunsmithing skill. This required analyzing the work and breaking it down into small steps: a division of labor. Although the eyewitness accounts of the early Armory's production system are not detailed, they do explicitly describe a division of labor by type of operation to be performed instead of by the part of the gun being made, which was a more familiar way of dividing the work. Denison Olmsted's 1832 "Memoir of the Life of Eli Whitney" says

In England, the labor of making a musket was divided by making the different workmen the manufacturers of different limbs, while in Mr. Whitney's system the work was divided with reference to its nature, and several workmen performed different operations on the same limb.¹⁶

Thus, where a single handcraft gunsmith would turn, drill, and file a given lock part until it was finished to the point of fitting to the other parts, a worker in Whitney's armory would specialize in drilling, say, or filing or turning all of the different parts, in production lots of 500 or 1000. According to Olmsted

these parts passed through the hands of several different workmen successively, (and in some cases several times returned, at intervals more or less remote, to the hands of the same workman) each performing upon them every time some single and simple operation, by machinery or by hand, until they were completed.¹⁷

To enable his workmen to perform one "single and simple operation" at a time, it is thought that Whitney devised a series of what are today called "jigs and fixtures". These fixed the parts and tools into their relative positions for each operation so that the cutting of the part by the tool would be correct.¹⁸ A drilling jig, for example, is made so that the workpiece fits under or inside it in only one position, and the drill, passing through holes in the jig, can enter the workpiece at only the desired angles and locations. A filing jig would sandwich a lockplate, for instance, in such a way that the filer could file no farther than the edges of the jig. In the 1825 inventory jigs and fixtures are probably subsumed in the catch-all terms "apparatus" and "appurtenances." Drilling jigs were apparently called "caps," in the inventory and in the label of Whitney's drawing, "Caps for Drilling Heart holes, Tumbler holes & Bridles."

The 18-year interregnum at the Whitney Armory from 1825 to 1842 has been little studied. Under management by Whitney's nephews, Philos and Eli Whitney Blake, for the decade following Whitney's death, then by Whitney's estate trustees, Henry W. Edwards and James Goodrich, for another eight years, the Armory continued to produce flintlock muskets for the U.S. Ordnance Department. Benjamin Silliman noted in 1832:¹⁹

The machinery has great neatness and finish, and in its operation evinces a degree of precision and efficiency, which gratifies every curious and intelligent observer... The manufactory has advanced, in these respects, since it has been superintended by Mr. Whitney's nephews, the Messrs. Blakes, and to them it is indebted for some valuable improvements.

One extremely interesting piece of surviving Whitney Armory machinery has been tentatively ascribed to this period: the oldest known milling machine still in existence. Now on display at the New Haven Colony Historical Society, it was found in 1912 in the hayloft of the Whitney barn, and according to the local tradition as recalled by Eli Whitney III, had been made and used by Eli Whitney, Sr.²⁰ This tradition has been disproved by subsequent scholarship, for the machine is not identified in the 1825 probate inventory, and it is not suitable for hollow-milling, which is the only kind of milling recognizable from tool marks on pre-1825 Whitney-made muskets, as discussed above.²¹ The best present guess as to the date of the Whitneyville miller is around 1827. A plausible suggestion is that it was made as part of a program undertaken by the Blake brothers to update obsolete equipment at the Armory in order to fulfill the Ordnance Department contract that Eli Whitney obtained before he died.²²

The Whitney Armory milling machine shares some features with the "straight cutting" machine in use by 1827 at John Hall's rifle works at Harpers Ferry Armory, most notably, its self-acting and automatically stopping feed mechanism. Although it is now missing its belt-driven rotary cutter and the screw-driven moving platform to which the work was fastened, the Whitney Armory miller was capable, if it was indeed like the Hall straight cutting machine, of using either a shaped cutter or straight edged cutter, to produce not only flat surfaces, but also "a great variety of other surfaces both regular and irregular."²³

These milling cutters would perform the heavier metal-removing work, reducing the amount of necessary hand-filing to finishing touches only. The milling machine thus saved on files, which were an expensive item of equipment, and on the work time and experience necessary to produce the locks. According to John Hall, one boy attending three or four such machines could "perform more work than ten men with files, in the same time, and with greater accuracy."²⁴ If the Whitneyville milling machine resembled the Hall machine in operation, then it probably saved on files, skilled labor, and time at the Whitney Armory before it was rendered obsolete by a later generation of improved milling machines.

When young Eli Whitney, Jr. took over management of the Armory in 1842, he set about tooling up under his new contract from the U.S. government for making the model 1841 percussion rifle. Machinery and fixtures for making the 1822 contract flintlock musket had to be retooled or replaced in order to produce the lock and barrel of the new model. Whitney, Jr. had the good sense to hire Thomas Warner as foreman, who, as master armorer at Springfield Armory, had just been making the same kind of major changes there. Thomas Warner had spearheaded the drive to equip the Springfield Armory with a set of new, more precise machines and a system of gauging that made it possible for the first time to achieve, in the late 1840's, the long-desired goal of interchangeability of parts in military small arms.²⁵ Under his tutelage, Eli Whitney, Jr. equipped the Whitney Armory to do likewise.

Thus, his letter book shows drafts of letters in late 1842 and early 1843 like one to a Mr. Rendall at "the Chicopee Falls Shop" in Massachusetts, asking "When will the milling machine you are making be completed, the sooner the better, etc. etc."²⁶ If his father's Armory had lacked machinery for gunstocking, Whitney Jr. made sure he now obtained the latest improved model of Thomas Blanchard's gunstocking lathe, with the capability of roughing out and smoothing the stock in the same machine.²⁷ Besides the milling machine and the irregular lathe, another type of machine that Eli Whitney, Jr. had to obtain that his father had not used for making muskets was a gunbarrel rifling machine, to cut the shallow spiral grooves within the barrel bore of the 1841 rifle.

In late 1846 Samuel Colt asked Eli Whitney, Jr. if he could make 1000 revolvers for him—the Colt-Walker model that was later famous - in three months. By this time Whitney, Jr. was so well equipped that even though he'd never made pistols before, he confidently replied "I can make them....as soon as any establishment in the U. States except one of the public armories, and probably sooner since no Factory has machinery as complete as mine..." He added, however, that "The 1000 cannot be made in 3 months by Any Factory."²⁸

Colt supplied a model and some machinery from his defunct factory in Paterson, New Jersey, and in only six months the 1000 revolvers were finished.²⁹ A few years after this episode, Whitney, Jr. resumed production of revolvers again, this time on his own account. He was diversifying his business into production of civilian as well as military arms. Since Colt had taken the machinery specifically for pistol making with him to set up his new factory in Hartford, Whitney, Jr. had now to re-equip his Armory for pistol production.

For the civilian market, the rationale for absolute inter-changeability of parts was weaker than in production of military arms,³⁰ and Whitney, Jr. advertised "good and serviceable arms not to be subject to government inspection of gauges."³¹ By this time, the machine tool firms that were emerging in New England were offering machines that were more specialized and capable of much greater precision than those in Whitney, Sr.'s day. The machinery Whitney, Jr. obtained in the 1850s may have included the other surviving milling machine that is said to have been used at the Whitney Armory. It is a "Robertson's Miller," patented in 1852.³²

Whitney, Jr. seems to have continued to derive satisfaction from having a factory that was well-equipped with machines, perhaps more than were absolutely necessary. In 1854 he contemplated the possibility of setting up a small shop in Canada for assembling revolvers from parts made at Whitneyville, by outfitting an extra workforce of three men and a boy with "1 slabber, 1 engine lathe, 1 hand lathe, 1 small shaving machine, 2 polishing wheels..." all from "the machinery I have on hand." Although rather discouraged when looking back in 1855 on his 13-year career so far, he counted first on the positive side of things, his "machinery worth now 10 to 12,000 Dolls.," In a final diary entry in 1860 he remarks on having "bo't largely of gun machinery",³³ perhaps referring to the machinery he bought at the bankruptcy sale of the Robbins and Lawrence machine-tool company in Windsor, Vermont in 1857, with the intention of reselling what he didn't need at the Armory.³⁴

He also confided to his diary, "I hope to retire from business in 2 years - pretty much," but this was February 22, 1860, and 14 months later the Civil War broke out. With the proceeds of his sale of water rights to the New Haven Water Company, Whitney, Jr. built new buildings on the west bank of the river, equipped them with machinery for production of 1861 model rifle muskets for contracts with the United States and with Connecticut, expanded his workforce to 400 or more, and apparently stopped thinking about early retirement. After he reorganized the business in 1863 as a corporation named the Whitney Arms Company, it was another 25 years before he sold out and retired from arms making in 1888. After the war the Armory's workforce returned to a peace-time level, and Whitney Jr. advertised his excess "new and secondhand" machinery for sale in the summer of 1868. The capabilities of the machines offered - for milling or slabbing, edging, screwmaking, drilling, planing, turning, screw cutting, pistol- and gun-barrel rifling and boring, clamp-milling, and gun-stocking would, it is safe to guess, have impressed Eli Whitney, Sr. and his probate inventory takers of 43 years earlier.

The Whitney Armory buildings located on the east bank of the Mill River were used for forging and casting metal parts. The fires used in these processes were fueled by coal and charcoal kept in the storage sheds lined up at the foot of the steep slope up Whitney Peak. In the later period a building at the end of this line housed the annealing and case-hardening operations. It is thought that the Armory's small powder house and proofing house for testing barrels were also situated at the foot of this slope from the early period onwards, but their precise locations remain uncertain.

The forging shop was built by Eli Whitney, Sr. of traprock quarried from East Rock itself. Changes to its water-power system were made in 1820, 1848, and 1860. Inside, water-powered bellows blew the fires of forges set on stone platforms, each with an anvil nearby. At these forges, smiths heated steel and wrought iron rods, which they then hammered by hand into bayonets, ramrods, lock parts, and gun mountings. They used swages, or dies, to achieve the more complicated shapes. A swage is a pair of steel blocks containing cavities in the shape of the upper and lower halves of the desired object. When the end of the heated rod or bar was held between them on the anvil and hammered, it would deform into the shape of the swage cavity. With a series of progressively detailed swages, it was possible to change the shape of the iron bar gradually. Later, waterpowered drop forging machines augmented the smiths' efforts. The forge building lasted well into this century, although it was converted to other uses, with a thick concrete floor covering the forge platforms. It was burnt out by vandals in 1950 and its remains were bulldozed into oblivion in 1970. In 1974, however, archeologists dug where the old pictures and maps showed the forging shop to have been, and excavated some of the forge platforms and the tail race of its water-power system before they had to bury it again.

In Whitney Armory days, coal and charcoal arrived by scow at the "sea-coal wharf located near the forge, and by wagon. Of the fuel shortage sheds, Benjamin Silliman wrote in 1832,

There are two buildings for fuel; the one for charcoal, and the other for mineral coal; both are finished with great exactness, by selecting smooth natural faces of the trap rock, which are accurately laid in mortar and carefully pointed; the floors are also of firm stone, laid with equal exactness. These store houses stand by the side of the mountain and its foot, and by excavating a road in the bank above, the coal carts are driven up to the gable end of the building, and their loads are discharged into them simply by tipping up the cart.³⁵

The fuel storage sheds, which were probably built at the same time as the forge shop, were remodeled for various purposes after gun-making ended at the site. The surviving shed, in which charcoal was stored for the Armory, has also been known as "the carpenter shop" and, when the Heany Laboratories occupied the site in the twentieth century, as "the transmission shop." But we can still see the heavy stone lintel high in the back wall, where charcoal was dumped through an opening provided in the original design of the building.

A large single-story wooden structure with a monitor roof, the foundry was probably built by Eli Whitney, Jr. at the start of his career at the Armory, when he was tooling up for production of the model 1841 U.S. rifle. Whitney, Jr.'s foundrymen cast gun fittings and pistol frames both of brass and of malleable cast iron, melting them in graphite crucibles inside a long, low furnace, or (for larger batches of iron only) in a high-standing furnace called a cupola. In the 1880s the foundry ceased operation and was used for storage until it was taken down early in this century. The cupola remained standing for years afterward.

An important part of the craft of iron metallurgy is heat-treatment to obtain the
desired degree of hardness and strength. Forged iron lock parts that had been machined and filed on the west bank of the river were case-hardened by packing them with carbon inside iron boxes, and holding the boxes at red heat for several hours. Carbon diffused a short distance into the iron, and upon quenching, made the surface of the parts hard. In a completely different process, iron castings from Eli Whitney, Jr. s foundry were annealed by heating in ovens for several days at controlled temperatures. The carbon already in the iron was thereby converted to graphite, which left the castings malleable.

The ninety years (1798-1888) in which the Whitney Armory was in operation was a period of experimentation and change in the use of metals in manufacturing.³⁶ The managers of the Whitney Armory participated in that experimentation and change. At the beginning of the period, wrought iron was the main constituent of the muskets that Eli Whitney, Sr. and other arms makers were manufacturing. In his day, when steel could only be made in small batches by the cementation or crucible process, it was expensive and used sparingly in arms manufacturing. By the end of the ninety-year period, steel produced by Bessemer and open-hearth methods was rapidly superseding wrought iron for most purposes in arms manufacturing. Eli Whitney, Jr. was in the 1840s among the first to shift from wrought iron to crucible steel in the manufacture of barrels for his guns, and from the 1850s onwards successfully applied the little-understood technique of malleable iron castings to the production of pistol frames and rifle fittings.

A practically extinct species of metal nowadays, wrought iron is nearly pure iron, and is therefore distinct both from cast iron and from steel, which are alloys of iron and carbon. During the Whitney Armory time-span, wrought iron, also called "bar iron," was produced at rolling mills that were associated with blast furnaces early in the century and with puddling furnaces late in the century. The iron masters used rolling mills to supply manufacturers with bars and rods of the sizes they required. One of Whitney, Sr.'s earliest orders to Forbes and Adam, suppliers of rolled iron in the Salisbury district of northwest Connecticut, specified bars of widths 1 5/8, 2 1/2, and 4 1/4 inches, totalling 1000 pounds of "Salisbury best bloomed iron."³⁷ Later on, iron came to the Whitney Armory by way of New York City, from more distant sources in Pennsylvania and in England.

Bar iron was forged into trigger guards, lock parts, etc. in the forge shop as described above. It was also made into barrels. In the early period of the Armory, production of a gun barrel began by heating and hammering a flat iron bar called a "skelp", wrapping it lengthwise around a solid iron rod, and welding it into a cylinder.³⁸ Barrel forgers used water-powered trip hammers for this purpose. Eli Whitney, Sr.'s armory had a triphammer shop - probably in the west bank complex of buildings - containing two trip hammers by 1825. After the barrels were welded, they were ground to final shape and polished on the outside and bored on the inside, also in west bank buildings

The small amount of carbon in steel (.1% - 1.5%) makes it stronger and harder than wrought iron. The cementation and crucible steel used at the Whitney Armory through much of its 90 years came from Sheffield, England. It was bent into springs; it was hammered into ramrods and bayonets in the forging shop. In the 18405 Eli Whitney, Jr. adopted the use of steel for gun barrels, earlier than did the Springfield Armory. Toward the end of his career, the technique he was using was to bore a hole through a 2" diameter rod of steel one foot long, insert a solid iron rod, and then roll the steel tube out to barrel length in a rolling mill. This operation probably took place in the gun-barrel shop on the west bank of the river.³⁹

Properly speaking, brass is an alloy of copper with zinc, but copper-tin bronze was also sometimes called "brass." In 1803 Eli Whitney, Sr. improved the muskets he was producing under his first contract with the U.S. Ordnance Department, by making their pans of brass instead of iron, so they wouldn't rust in contact with the gunpowder, and in 1808 "caused a mould to be constructed of cast brass" for his friend Benjamin Silliman, who was professor of chemistry at Yale.⁴⁰ So we know that he had access to facilities for casting brass, but we do not know where they were located. By 1811, the brass industry in nearby Waterbury, Connecticut was getting under way.⁴¹ The rolling mills of that growing industry later made brass available to manufacturers in sheets of uniform thickness, enabling young Eli Whitney, Jr. in 1842 to ponder whether to make the barrel bands and other fittings for the 1841 military rifle of cast brass, or of sheet brass. He opted for casting the bands and other fittings "in my own furnace," and hired a brass caster.⁴² In the foundry that Whitney, Jr. built, brass was melted in crucibles made of clay and graphite, and poured into sand moulds of the proper shapes for the various gun fittings, and for frames of some models of pistol. After cooling, which was rapid for small objects, the brass gun fittings were broken out of the casting sand and the extraneous pieces of brass "gating" broken or sawed off, to be recycled through the melting process. The castings were polished in a tumbler and taken to the west bank buildings to be machined and assembled with other gun parts into a completed weapon.

On many models of military and civilian weapons, fittings were not of brass but of iron. Although forging was the usual technique for shaping iron into fittings, by Eli Whitney, Jr.'s day, an alternative method was available that had been developed in the late 18205 in Newark, N.J., namely, "black-heart" malleable iron casting (named for its appearance when fractured). Ordinary cast iron, which contains 1.5% to 5% carbon, is brittle and therefore an unsuitable material for any object to be hammered during manufacture or use. But prolonged annealing of castings made with iron having an appropriate composition, under controlled temperatures and atmospheric conditions, converts the carbon to graphite, making the castings malleable. Malleable iron castings were adopted for iron work on carriages, where it eventually supplanted wrought iron.

It was perhaps through the carriage industry, which was strong both in Newark and in New Haven, that the technique of making blackheart malleable cast iron spread from New Jersey to Connecticut, and came to the attention of Eli Whitney, Jr. He adopted it for making pistol frames and fittings for long arms in the late 18505 and early 18605. He was able to use the same kind of crucibles and furnace as for brass casting, but he also built a cupola, which was suitable only for melting iron. The malleable iron castings were as strong as wrought iron gun parts and could be drilled and milled as well. They were apparently not case-hardened, as wrought iron parts were. Malleable cast iron did not replace wrought iron for all purposes in Whitney arms: many items, such as hammers, trigger guards and receivers for rifles, continued to be forged and case-hardened after machining.⁴³

1. Eli Whitney, "The Manufacture of Firearms," 1812 memoir, Eli Whitney Collection,YUA.
2. American Slate Papers II, #263, pp. 756-57.
3. American State Papers II, #246, p. 538.
4. The very old milling machine from the Whitney Armory that has survived and was long thought to have been made by the elder Eli Whitney, is now deemed by historians of technology to date from somewhat after his death. See discussion of "Middle Armory Period".
5. Letter, Eli Whitney to Oliver Wolcott, i May 1798, Eli Whitney Collection, YUA.
6. Letter, Philos Blake to Betsy Blake, 7 September 1801 (Original spelling), Eli Whitney Collection, YUA.
7. Timothy Dwight, Travels in AVi/> England and New York, (New Haven, 1821), vol. II, Letter I, describing a trip begun September 20, 1803.
8. Two nearly identical versions of this inventory exist in the Eli Whitney Collection.
9. Letter, Eli Whitney to Oliver Wolcott, i May 1798, Eli Whitney Collection, YUA.
10. Letter, Eli Whitney to Irving, 14 November 1807. Eli Whitney Collection, YUA.
11. Account book, p. 122, lx)X 9, folder 0163. Eli Whitney Collection, YUA.
12. Robert Woodbury, 'The Legend of Eli Whitney and Interchangeable Parts, Technology and Culture \ (1960), p. 249.
13. Colonel John Whiting, report on Springfield Armory, 31 December 1809, in James E. Hicks, United Slates Ordnance (Mount Vernon, N.Y., 1940), vol. 2, p. 131.
14. Edwin Battison, "Eli Whitney and (he Milling Ma-ch'mc," Smithsonian Journal JHistoiy i (1966), p. 23.
15. Ibid., p. 32.
16. Denison Olmsted, "Memoir of the Life of Eli Whitney,"
    American Journal of Science and Arts XXI #2(1 832), P- 43-
17. Ibid., p. 43.
18. E.G. Parkhurst, "Manufacture by the System (^"Interchangeable Vans," American Machinist 24 (3 January, P-39-
19. Benjamin Silliman, "Reminiscences of the late Mr. Whitney," American Journal of Science and Arts XXI #2 (1832), pp. 55-56.
20. Joseph W. Roe, "History of the First Milling Machine, American Machinist (27 June 1912), pp. 1037-38.
21. Unknown
22. Edwin Battison, "A New Look at the 'Whitney' Milling Machine," Technology and Culture 14 (1973), p. 597-
23. James Carrington, report, 1827, quoted in Merritt Roe Smith, "John H. Hall, Simeon North, and the Milling Machine: The Nature of Innovation among Antebellum Arms Makers," Technology and Culture 14
24. Ibid., p. 582
25. Charles H. Fitch, 'The Rise of a Mechanical Ideal," Magazine of American History (June 1884)15 16-27.
26. Letterbook, box 6, folder o i 72, Eli Whitney Collection, YUA.
27. Letter, Eli Whitney, Jr. to Thomas Blanchai d, 20 December 1842, Eli Whitney Collection, YUA.
28. Letter, Eli Whitney, Jr. to Samuel Colt, 25 December 1846, Eli Whitney Collection, YUA.
29. Samuel Colt to William L. Marcy, 6 July 1847, in John E. Parsons, ed., Sam Coil's Gum Record (Hartford: Connecticut Historical Society, 1949).
30. Robert A. Howard, "Interchangeable Parts Reexain-inecl: The Private Sector of the American Arms In-clustry on the Eve of the Civil War," Technology and Culture 19 (1978), pp. 633-49.
31. Norm Flayderman. I-'la\dei man's Cuide to Antique A mer-ican Firearms (Northlield, III.: D.B.I. Books, 1977), P- ^7-
32. Robert S. Woodbury, History of the Milling Machine (Cambridge, Mass.: M.I. I". Press, 1960), pp. 35-36.
33. Business diary entries, September 1854, 22 December 1855, 22 February 1860, box 1 1, folder 0173. Eli Whitney Collection, YUA.
34. Flayderman, o{>. cit.. p. 23 1 .
35. Benjamin Silliman. "Reminiscences of the late Mr. Whitney," American Join rial of Science and Arts, Vol. XXI (1832), p. 57.
36. Robert B. Gordon, "Materials for Manufacturing:
37. Kenneth T. Howell and Einar W. Carlson, Men of Iron: Forbes and Adam, (Lakeville, Conn.: privately printed, 1980), p. 88.
38. Merritt Roe Smith, Harpers Ferry Armory and the New Technology, (Ithaca: Cornell University Press, 1977), p. 94.
39. William P. Blake, History of the Town of Hamden(New Haven: Price, Lee & Company, 1888), p. 141.
40. Stillman, "Reminiscenes," op. cit., p. 60.
41. Cecilia Bucki et al, Metal, Minds and Machines, (Waterbury, Connecticut: Mattatuck Historical Society, 1980).
42. Letters, Eli Whitney, Jr. to Lt. Col. Talcott, Ordinance, 21 December 1842, to R. Johnson, Jr., 20 December 1842, to Blunt & Lynes, 27 December 1843, letterbook, Eli Whitney Collection, YUA.
43. C.C. Cooper, R.B. Gordon, and H.V. Merrick, "Archeological Evidence of Metallurgical Innovation at the Eli Whitney Armory," IA, the Journal of the Society for Industrial Archeology), 8 (1982), pp. 1-12.