ELISHA MITCHELL SCIENTIFIC SOCIETY. 9 
acidity of the violet and green solutions, it was seen that 
both solutions were acid. We tried a large number of 
the usual indicators, but the violet and green colors of 
the solutions interfered too much to give any results 
with them which could be regarded as at all satisfactory. 
It was fonund that fair resuits could be obtained by using 
a decinormal solution of ammonia and noting the first ap- 
pearance of a permanent precipitate. 
Tenth-normal 
ammonia. 
ie 
Per etais it MA Ce, Cold: Treqaired ie ot. en 27.5 
ef see nth. 6) boiled onernelh hour }oc (Le. dol 27.6 
a + ap: pO. Sti ceeneie TAGE ee i tw es 26,5." 
te bk Alege Nee AL MRE ol Fg PR a ee Re 26.5 
During the boiling, the water evaporated was repeatedly 
restored. Unless this was done a little acid was lost, 
and even with this precaution there was a small loss, and 
this may explain the acidity of the vapors coming off at 
at 100° as observed by Recoaru. 
The experiments therefore agree with those of Baub- 
igny and Pechard, but are at variance with the conclusions 
ef the’other authors mentioned. We think the experi- 
mental data of these authors do not afford sufficient and 
satisfactory evidence to serve as a basis for their conclu- 
sions that free sulphuric acid exists in the solution. The 
methods adopted are very indirect and the results capa- 
ble of other explanations. 
THE EXISTENCE OF CHROMO-SULPHURIC ACIDS. « 
Several articles have been published by Recoura’ upon 
chromo-sulphuric acids. He claims to have prepared 
several of these and regards the formation of such bodies 
as a probable explanation of the change 1n the green so- 
lutions, and others, as Whitney and Dougal, seem to ac- 
cept his explanation. Recoura thinks there are two 
isomeric modifications of chromium sulphate; one violet, . 
one green, and also another green sulphate not isomeric, 
