48 Proceedings of the British Association. 



Prof. Thomas Thomson communicated an account of the most 

 important chemical manufactures carried on in Glasgow and the 

 neighborhood. 1. Iron. The quantity of iron smelted here 

 cannot be much less than 200,000 tons, nearly a fifth part of all 

 the iron smelted in Great Britain. The ore employed, is the car- 

 bonate of iron, or clay iron-stone. The rapid increase of iron- 

 smelting has been the consequence of a discovery of Mr. Neilson, 

 manager of the gas works. This is now universally known un- 

 der the name of the hot blast. The air is heated to more than 

 607° before it enters the furnace, by passing through a range of 

 heated pipes. Under this treatment, coals may be used without 

 previous coking, and instead of seven tons of coals for every ton 

 of cast iron, three tons or even two and a half, will suffice. 2. 

 Sulphuric acid. The manufacture of this acid was begun by 

 Dr. Roebuck, at Prestonpans, about 1763, but it is now more than 

 20 years since his manufactory was abandoned. The sulphuric 

 acid works, at St. RoUox, on the banks of the Monkland canal, 

 were begun about 45 years ago. They were at first upon a very 

 small scale, but they are now probably the largest of the kind in 

 Europe. The size of the leaden chambers was gradually increa- 

 sed, and the substitution of steam for the water formerly placed 

 at the bottom of the chambers, was a vast improvement. The 

 sulphur is burnt over a stove, and an iron cup containing the re- 

 quisite quantity of saltpetre, mixed with the requisite quantity of 

 sulphuric acid, is placed over the burning sulphur. By this 

 contrivance the sulphur is completely converted into sulphurous 

 acid, and the whole of the nitric acid carried along with it into 

 the leaden chambers. The acid which collects at the bottom 

 of the chambers, has a gravity of 1.75 ; or it is a compound of 

 one atom anhydrous acid, and two atoms water. This acid is 

 concentrated by heating it in a platinum still, till the second atom 

 of water is driven off. When in full work, the quantity of sul- 

 phuric acid made in it, exceeds 300,000 pounds avoirdupois per 

 week. Forty five years ago, it cost eight pence per pound ; 

 the present price is under a penny a pound. 3. Bleaching pow- 

 der. One of the great purposes to which sulphuric acid is ap- 

 plied at St. Rollox, is the manufacture of bleaching powder, or 

 chlorite of lime, as it is now called. The requisite mixture of 

 common salt, binoxide of manganese, and sulphuric acid, is 

 put into a leaden still, and the chlorine evolved passes through 



