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- 

 phuric 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 Measurements. 



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 c.c. 

 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 2 SO 4 and CuSO 4 , and K 2 S0 4 and H 2 SO 4 , 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. Sci., VOL. X. TRANS. N. 



