214 CHEMICAL MANUFACTURES IN GLASGOW, ETC. 
Dr. Thomson believes, the process 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 
which 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 sulphuret- 
ted hydrogen is evolved, the bad effects of which on the 
workmen, are obviated by setting it on fire, and allowing it 
it to burn as it is extricated 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 ex- 
ceed 190° or 200° at most. The iodine passes into the re- 
ceiver which consists 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 manufacture universally known ; but soap of a very su- 
perior 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 9.75cwt. of tallow, 
3.25cwt. of rosin, 4cwt. of soda ash, equivalent to 2cwt. of 
soda, mixed with the requisite quantity of water; the white by 
boiling 13cwt. of tallow, 4cwt. of soda ash in the same manner. 
Tallow, which is a compound of two oily acids and glycyffrine, 
undergoes decomposition, and the soda combines with the acid 
and forms soap. When the combination is complete, a quanti- 
ty 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 frames, where it is allowed 
