272 Proceedings of Royal Society of Edinburgh. [april 2, 
XVI. Zinc - Iron - Ammonium Sulphate. — 12 grammes (‘04 
equivalent = HAS) zinc sulphate were mixed with 11 grammes 
(*04 equivalent = 11-12) ferrous sulphate, together with 11 grammes 
(*08 equivalent = 10-56) ammonium sulphate. Four crops — XYIa, 
XVI/?, XV ly, and XVI8 — were collected. 
In the analyses of all these four crops, and also in those of XVII. 
and XVIII., the following method for the separation of the iron 
and zinc was rigidly adhered to, a fact on which I lay special stress. 
In order to convert the iron into the ferric state, the substance was 
evaporated to dryness with nitric acid and dissolved in water with 
the addition of a few drops of hydrochloric acid. The iron, after 
addition of sodium carbonate to neutralisation and then of sodium 
acetate, was, by boiling, thrown down as basic acetate. This latter 
was dissolved in hydrochloric acid, and the iron reprecipitated by 
ammonia. The zinc in the filtrate from the basic acetate was estimated 
as in II. As a check, the iron was occasionally estimated by 
tritration with standardised permanganate solution. 
XVII. Zinc - Iron - Ammonium Sulphate. — The component 
sulphates in this case were mixed in the same quantities as in XVI. 
One crop only was collected. 
XVIII. Zinc-Iron-Ammonium Sulphate. — 28 grammes {'1 
equivalent = 27-8) ferrous sulphate and 29 grammes (-1 equivalent 
= 28-7) zinc sulphate were dissolved in water with the calculated 
quantity of ammonium sulphate. Eight crops were collected. 
Each crop was, weighed. The weights in grammes were: — 
a = 3-5, y8 = 2-9, 7 = 3-0, 8= 2-1 
€= 1-2, C = '9, 0 = 2-6. 
XIX. Magnesium-Iron- Ammonium Sulphate. — 12 grammes 
(*05 equivalent = 12-3) magnesium sulphate were mixed with 14 
grammes (-05 equivalent = 13 -9) ferrous sulphate and the calculated 
quantity of ammonium sulphate. One crop was collected. 
XX. Magnesium-Iron-Ammonium Sulphate. — The components 
were mixed in very nearly the same quantities as in XIX. Seven 
crops were collected, the first three of which were weighed — 
a=Tl; y8 = 3; y = 2-3. 
In this case and also in XIX., the iron was estimated as described 
in XV. 
