Chemistry. xlvii 
7. Ferro-chyazic Acid.—Mr. Porrett has discovered a method 
of procuring this acid in the state of crystals. He dissolves 58 
grains of tartaric acid in alcohol, and mixes the solution with a 
solution of 50 grains of prussiate of potash, dissolved in two or 
‘three drachms of hot water. The potash and tartaric acid se- 
parate in the state of bitartrate of potash. The alcoholic solution 
retains only the ferro-chyazic acid, which, by spontaneous eva- 
poration, is deposited in the state of small cubic crystals. (An- 
nals. of Philosophy, xii. 216.) 
When I published my experiments on the composition of 
ferro-chyazic acid, I was far from considering the results which 
{ obtained as precise, as will obviously appear to any one who 
takes the trouble to peruse the paper in question. But my rea- 
son for publishing them was, that they were as accurate as I 
could make them with the kind of apparatus which I employed. 
T have since modified and improved this apparatus considerably ; 
but have not yet brought it to a degree of precision on which 
full confidence can be put. But I expect very soon to be pro- 
vided with one possessed of all the requisite precision. As soon 
as this is the case, I shall repeat my experiments again, and 
flatter myself that the result will be more satisfactory. Mr. 
Porrett has favoured us with an analysis, which is certainly more 
likely to be accurate than mine, as it agrees with the atomic 
theory. But from the many experiments which I have made on 
the analysis of combustible substances by means of peroxide of 
copper, I am satisfied that we cannot venture to draw conclu- 
sions from one solitary experiment, without the utmost hazard 
of deceiving ourselves. 1 shall not make any observations on 
the weights of atoms used by Mr. Porrett in his calculations, 
though | have no doubt that they are less precise than those 
which I employ, because I propose to return to this subject in 
a future paper. 
8. Purpuric Acid.—This is the name given by Dr. Wollaston 
to a new acid discovered by Dr. Prout, and formed by the action 
of nitric acid on uric acid. The process by which this acid may 
be obtained is as follows : 
Dissolve pure uric acid in dilute nitric acid; after the solution is 
completed, saturate the excess of nitric acid with ammonia, and 
then slowly concentrate by evaporation. As the concentration 
advances, the liquid becomes dark coloured, and dark red gra- 
nular crystals soon separate in abundance. ‘These are crystals 
of purpurate of ammonia. These crystals are to be dissolved in 
pound of 2 atoms sulphur and 1 atom of hydrocyanic acid; or its constituents 
may be represented thus: 
2 atoms sulphur...... ....- =4 
2 atoms carbon.,........... = 15 
WEALGM BZOLC. ic iciencinipee aes = 1°75 
I atom hydrogen............ = 0°125 
7°375 = atom ef sulpho- 
ehyazic acid.—(See Annals of Philosophy, xiii, 356.) 
