48 ROYAL SOCIETY OF CANADA 
The second stage is the fundamental principle on which Kopp’s 
soda process is based.! This process has been approved by Stromeyer ” 
but condemned by Hoffman, Waldeck and Lunge. The main features 
objected to are the destructive action of the mixture of sulphate of 
soda, ferric oxide and coke upon ordinary furnace linings; and the 
impossibility of recovering a high percentage of the total soda, as 
carbonate. The first objection is met by Macfarlane * who describes 
a furnace lining of quicklime and basic slags, impregnated with 
sodium sulphide. The second disadvantage is avoided by another of 
Macfarlane’s claims, according to which the carbonating is done by 
furnace gases during the lixiviation. 
The third stage, involving the decomposition of ferrous sulphide 
by hydrochloric acid, with formation of ferrous chloride and sulphur- 
etted hydrogen presents no difficulties. 
The fifth stage, in which sulphuretted hydrogen is burned to 
furnish SO,, for the leaden chambers in the manufacture of suplhuric 
acid, is equally free from practical difficulties.* 
The object kept in view throughout these experiments, and that 
which furnished a motive for the work, was the demonstration of 
conditions necessary to make the reactions of the fourth stage prac- 
tically successful. 
Recorded attempts to produce chlorine by the oxidation of chloride 
of iron are the following: 
Thibierge (Eng. pat. 2290, 1855) proposes to pass dry air over 
ferrous chloride; but I cannot find that the process has ever been 
investigated under the conditions of his patent. The same reaction 
is utilized by Macfarlane (1863) and by Longmaid, Konigs, Henderson 
and others. In no case, however, does it appear that the process has 
been subjected to a full and searching investigation; and it was 
through Mr. Macfarlane that I was led to enter upon the work now 
put on record. I have had the advantage of consultation with Mr. 
Macfarlane throughout the progress of the investigation, and it is 
largely due to his encouragement and assistance that I have been able 
to carry it to a successful conclusion. 
I may here draw attention to the fact that the patents of Swin- 
dells and Nicholson (Eng. pat. 390, 1852), and of Larkin and White 
(Eng. pat. 3093, 1870) treating of the production of chlorine by 
oxidation of chloride of iron, refer to the per-chloride, and are to be 
distinguished from those previously mentioned. 
1 Ann. Chim. Phys., Sept., 1856, p. 21; and Lunge, Sulphuric Acid and 
Alkali, 2nd Edition, III., 223. 
2 Ann. Chem. Pharm., CVII., p. 333. 
3 Engl. Patent 126, 1863. 
* Lunge, Sulphuric Acid and Alkali, I., 277. 
