AND COPPER SULPHATE—LINDSAY. 209 
I also made a number of determinations, using standard 
ammonia in place of the standard potash, but although the pre- 
cipitating point could be fairly well determined, the results did 
not agree as well with the amount of sulphuric acid known to be 
present. 
We thus see that this method of chemical analysis for sul- 
phurie acid, while it gives us a good method of analysis for such 
mixtures, sheds no light on the presence of acid sulphate in 
solution. 
While any recognizable decrease in the amount of sulphuric 
acid given up to analysis from that known to be present, would 
yield an almost conclusive proof of the presence of acid sulphate, 
the result obtained here, does not of necessity lead to the reverse 
conclusion. 
Specific Gravity Measwrements. 
All specific gravity measurements were made at 18°, and are 
referred to water at 18°. In these measurements, a pycnometer 
of the form recommended by Ostwald, and holding about 25 ce. 
was used. 
The pycnometer was brought to 18° by being placed in a 
water bath, provided with a mechanical stirrer, whose tem- 
perature could easily be kept constant to 1/20 of a degree. 
When the liquid had come to the temperature of the bath, the 
meniscus was brought to the mark, the pycnometer taken out, 
dipped in distilled water, dried carefully with a linen towel, and 
weighed. 
From several successive measurements of the same Solution, 
it would appear that my measurements of density might be in 
error by about 5 in the fifth place of decimals. 
Favre and Valson* have found that, in the case of concentra- 
ted'solutions of K,SO, and CuSO,, and K,SO, and H,SO,, the 
density of a mixture of equal volumes of the constituents, is less 
than the mean value of their densities. From these results they 
*Compt. Rend., 77, 907. 
Proc. & TRANS. N. S. Inst. Scr., Vou. X. TRANS.—N. 
