50 Proceedings of the British Association. 



that time it was prepared only in laboratories for scientific purpo- 

 ses, and sold at a high price. Mr. Mackintosh introduced it to the 

 calico-printers, who use it extensively, to produce very beautiful 

 blues and greens. It is prepared by burning the hoofs and horns 

 of cattle with potash, and some iron in iron pots. The hoofs and 

 horns of a hundred head of cattle are consumed in the works ev- 

 ery day. After combustion the residue is lixiviated with water, 

 and when the solution is sufficiently concentrated, the prussiate of 

 potash crystallizes. Connected with this manufactory is one of 

 Prussian blue. It is made by mixing sulphate of iron, alum, and 

 prussiate of potash, and precipitating.the whole by an alkali. The 

 precipitate is at first li^ht blue, but it is washed with new portions 

 of water every day for several weeks. At every washing the 

 color deepens, and when it has acquired the requisite shade, the 

 Prussian blue is allowed to subside, the water is drawn off, and the 

 powder permitted to dry. The color varies according to the propor- 

 tion of alum employed, and it has the finest color of all, with the 

 coppery lustre which is so much admired, when no alumina what- 

 ever is mixed with it. 7. Bichromate of potash, a salt very 

 much used by calico-printers, and forming the finest and most in- 

 delible yellows, oranges, and greens, is made at the manufactory 

 of Mr. White, at Shawfield, near Rutherglen, about two miles 

 from Glasgow. Its introduction constituted quite an era in cal- 

 ico-printing. It formerly cost a guinea an ounce ; it is now sold 

 at two shillings a pound. Tartaric add is also made here. It is 

 largely used by the calico-printers, chiefly to disengage the chlo- 

 rous acid from bleaching powder, and enable it to destroy the co- 

 lor on particular parts of the cloth, either that these parts may re- 

 main white, or that some other color may be superadded. It is 

 obtained from cream of tartar, by throwing down the tartaric acid 

 by means of lime, and afterwards decomposing the tartrate of 

 lime by means of sulphuric acid, and crystallizing the tartaric. 

 At the same manufactory the carbonate of soda is converted by 

 exposure in an atmosphere of carbonic acid, into sesquicarbonate. 

 It is chiefly used by the makers of soda water. Among other 

 manufactures and processes carried on at this place, were men- 

 tioned acetic acid from wood ; iodine ; soap ; bleaching of cot- 

 ton cloth; Turkish red dyeing; calico-printing; glass making; 

 starch making, &c. 



