208 SOLUTIONS OF SULPHURIC ACID 
It is thus seen not only that the precipitating point is a per- 
fectly definite one, but that it can be determined with consider- 
able accuracy. 
The next question is, whether it expresses accurately the 
amount of acid present. 
Concentration. He S04 | 
f=. Error 
He SO4 CuSO4 Calculated.| Found. 
416 064 2036 .2039 + .15% 
217 127 . 1356 .1357 +.08% 
Column I. contains the concentration of H,SO, in mixture in 
eramme-molecules per litre. 
“« II. contains the concentration of CuSO, in mixture in 
geramme-molecules per litre. 
“ III. contains the amt. of H,SO, in grammes, calculated to 
be in every 5 cc. of mixture. 
“ JV. contains the same, as found in every 5 cc. of mixture. 
« —V. contains the percentage error. 
We thus see that by this means, the sulphuric acid present 
can be determined with considerable accuracy. 
In the above analyses, the mixture under analysis was dilu- 
ted very much, the reason being, that so far the work has been 
only to find a good method of analysis, and not to prove or 
disprove the presence of acid sulphate. 
But now a number of analyses were performed on the above 
mixtures, keeping the mixtures concentrated, and in no case was 
there any appreciable difference in the amount of caustic potash 
needed before precipitation would commence. 
The results obtained from analyses of the concentrated mix- 
tures, gave, as a rule, slightly less quantities of sulphuric acid. 
But this I would attribute to the fact that the precipitate would 
be more easily noticed in the smaller volume than in the larger. 
