TRANSACTIONS OF THE SECTIONS. 63 
foreign bodies with which it is impregnated, the acetic acid being 
capable of resisting a higher temperature without decomposition than 
most compound vegetable bodies. The acetate of lime thus purified is 
decomposed by sulphuric acid, and the acetic acid obtained by distilla- 
tion. By this process it may be obtained very strong. The author 
possesses it composed of one atom acetic acid, and one atom water. 
When of this strength it crystallizes in winter, but becomes liquid 
again in summer. In the same manufactory there is another liquid 
prepared, namely, pyroxylic spirit, now well known. A most interest- 
ing set of experiments on it has been made by Dumas, who has di- 
stinguished its basis by the name of methylene, and has discovered 
various new compounds which it is capable of forming. 
9. Another chemical manufacture of considerable importance, and 
which the author believes to be peculiar to Glasgow, is iodine. A few 
years ago there were no fewer than ten manufactories, in each of 
which it was made to a considerable extent; but as iodine is only used 
in medicine, the sale is necessarily limited, and most of these works are . 
nowabandoned. The process followed by all the makers was, Dr. Thom- 
son believes, the contrivance of Mr. Macintosh. Iodine is made from 
kelp, and it deserves attention, that those kinds of kelp that contain 
most potash, contain, at the same time, the most iodine. The kelp is 
lixiviated, and all the salts that can be extracted from the solution by 
evaporation are separated. The mother water remaining is now mixed 
with an excess of sulphuric acid. A great quantity of sulphuretted 
hydrogen is evolved, the bad effects of which on the workmen are 
obviated by setting it on fire, and allowing it to burn as it is extracted 
from the liquid. To the liquid thus freed from sulphuretted hydrogen 
and from muriatic acid, a quantity of binoxide of manganese, equal in 
weight to the sulphuric acid employed, is added. The whole is put 
into a leaden still, and heated to a temperature which must not exceed 
190° or 200° at most. The iodine passes into the receiver, which con- 
sists of a series of spherical glasses, having two mouths opposite to 
each other, and inserted the one into the other. 
10. It may seem superfluous to mention soap, because it is a manu- 
facture universally known; but soap of a very superior quality is made 
in Glasgow. The number of soap-works amounts to seven, and one of 
these, that at St. Rollox, is the third, if not the second, in point of 
extent, in Great Britain. The ingredients of soap are soda, tallow, 
and rosin, and sometimes palm-oil. Two kinds only of hard soap are 
made here, namely, yellow and white. The yellow soap is made by 
boiling 9°75 cwt. of tallow, 3°25 cwt. of rosin, 4 cwt. of soda ash, 
equivalent to 2 cwt. soda, mixed with the requisite quantity of water ; 
the white, by boiling 13 cwt. of tallow, 4 ewt. of soda ash in the same 
manner. Tallow, which isa compound of two oily acids and glycerine, 
undergoes decomposition, and the soda combines with the acid and 
forms soap. When the combination is complete, a quantity of common 
salt is put into the hot liquor. It dissolves in the water, and the soap 
separates, and swims on the top. It is now allowed to cool to 150° at 
an average, and then taken out in a liquid state, and poured into 
