356 SOME OF THE RELATIONS OF SALTS OF ZINC AND ALUMINA 
potassa, — a quantity to which 0.1173 gram. sustains the relation of 3: 3.81, or nearly 
of 3:4. It is obvious, therefore, that the chief part of the precipitate was the well- 
known compound 4 ZnO . SO,. 
Resolution was attended with much greater difficulty. The results were so variable, 
that no confidence could be placed in them. ‘The influence of water was observed here 
as in the experiments with soda. ‘The potassa was too dilute. 
A more concentrated solution, of which 1 c. c. contained 0.2590 gram. of potassa, gave 
the following result. : 
10 c. c. of solution of ZnO . SO; required 4 c. c. of solution of KO to precipitate and 
re-dissolve. Allowing, according to the preceding determination, .75 of an equivalent 
for the precipitation, there are required to re-dissolve 2.65 equivalents. 
Bonnet dissolved two parts of hydrated oxide of zinc in five parts of potassa solu- 
tion of 1.3 specific gravity. Such a solution contains about .25 part of KO. 5c.c. 
would contain 1.25 grammes, which would give about two atoms of zinc dissolving in 
11 of potassa; or the soluble compound would be 8 ZnO.5 KO. The compound is 
probably that obtained by Fremy,* — two atoms of oxide of zinc to one of potassa. This 
compound, upon the slightest addition of water, resolved itself, according to Fremy, 
into anhydrous oxide of zinc and hydrated potassa. These facts sufficiently explain 
the difficulty of obtaining satisfactory results in the attempts to re-dissolve with a 
solution of the strength here employed. 
Experiments with Sulphate of Alumina. 
Common potassa alum, refined by repeated crystallizations, was dissolved in distilled 
water. 
Lee of the alum solution contained 0.0371 gram. of crystallized potassa alum. 
“ S x p. c 0.009386 « SO;, combined with alumina. 
* wc Sone = « 0.0430 « NaO. 
S * ^. potassa a s 00280 * KO. 
" * sulphuric acid i s 0.03264 g SO;. 
« * chloride of ammonium * « 0.08305 e NH,4CI. 
Experiments with Soda. 
Alum. MEI Sedis v periurii: MRNA 
precipitate. and re-dissolve. re-precipitate. to re-precipitate. 
10 c. c. 1.4 2.7 ^ 1.0 2.9 
S CK 1.4 2.7 1.0 2.9 
20 c. c. 2.8 5.4 2.0 5.8 
EE 2.8 5.4 2.0 5.8 
Average, 10 c. c. 1.4 2.7 1.0 29 
* Compt. Rend., XV. p. 1106. 
