1016 
PROFESSOR J. W. MALLET ON A REVISION 
tained that exposure over sulphuric acid led to large loss of water of crystallisation 
within a short time. It was found, however, that even in the air loss of weight went 
on for so long a time that it could not possibly be referred to mechanically adherent 
water only. It is true that this loss fell off very rapidly after the first hour or so, but 
it was impossible to decide precisely when it began to affect the water of crystallisation. 
In order to fully exhibit this I cpiote the following results obtained from a single large 
specimen kept very long on hand in a place carefully guarded against dust. 
Original weight of alum after one hour’s exposure to the air at 22 0, 5 C 
Loss of weight in 1st twenty-four hours . 
3 3 ?? ......... 
33 5 5 . 
2 nd 
3rd 
55 
55 
35 
5 3 
55 
4th 
5 th 
5 5 
3 3 
6 th 
7 th 
8 th 
9th 
10 th 
33 
33 
33 3 3 
3 3 3 3 
Grms. 
35'7456 
•0088 
•0025 
•0017 
•0015 
•0010 
•0012 
•0009 
•0011 
•0007 
’0005 
This series of weighings was carried on at longer intervals for six months more ; the 
monthly loss was at first '0087 grm., gradually fell off, became as small as '0006 grin, 
in one month of cold weather when the temperature of the room was unusually low, 
and again rose, with warmer weather, to '0012 grm. for the sixth and last month for 
which the weighings were continued. It was further found that, on placing some of 
the small crystals of the alum in a glass vessel deep enough to prevent mechanical 
loss, sensible loss of weight could be produced by the heat developed in simply 
crushing and pulverising the salt with a thick square-ended glass rod used as a pestle, 
and weighed along with the glass and its contents. While, therefore, it might be 
assumed as probable that mechanically adherent water would be got rid of within a 
time during which but a very minute quantity of water of crystallisation would be 
lost, a slight doubt is thrown over the exact formula of the salt as analysed, in 
reference to this component. Some of the ignition experiments were made with 
specimens which had been dried by longer exposure to the air than others, as will be 
noted hereafter. 
In the second place it appeared that a minute trace of basic sulphate was retained 
by the alumina left after ignition at even a very high temperature. This could not 
be extracted by water, but was detectable by fusion with sodium carbonate free from 
sulphur, taking care to use an alcohol flame only. By moistening the alumina with a 
strong solution of pure ammonium carbonate, re-igniting, and repeating this treatment 
