164 
DR, H. T. BARNES ON THE CAPACITY FOR HEAT OF WATER 
original cells from the date of the last comparison given in Table VII., Section 25, 
p. 151 ( loc . cit.), to the close of the present series of experiments. Various other 
tables are given here in order for the other types of cells, and I have designated 
the different cells by capital letters indicating the type, and by a suffix to indicate 
the number of the particular cell. The crystal cells are given as X, the sealed cells 
by S, the inverted cells by XR, and the cadmium cells by Cd. In the original table 
of comparison already referred to, cells X l5 X 2 , X 3 , X 5 , X 0 , X 10 , and X n were given. Of 
these cells, all are at present in existence, with the exception of X 6 , which was taken 
away from the laboratory and since broken. Table I. may be taken as a continuation 
of the older table. The relative differences in these cells, although somewhat larger 
than is usually obtained in constructing a number of cells from the same lot of 
materials, have been maintained so consistently that over extended periods a constancy 
of 1 in 100,000 can be easily assumed. Later results show that cells X 2 and X 5 have 
lowered somewhat, but even in these two cases the drop is less than T mv,, and 
takes place so gradually as to be easily corrected for. It is highly probable that all 
these cells will eventually become lower in value as they become older, on account of 
the drying up of the crystals. 
During the winters of 1897-98 and 1898-99 a number of tests were made by some 
of the advanced students on cells prepared by themselves under my supervision. 
These cells were all subjected to a temperature cycle of 15° to 0°, to 15° to 30°, to 15°. 
The first batch of cells made during 1897-98 were in the inverted form, and were 
made in the usual way in a long test-tube for immersion in the water-bath. 
A 10 per cent, zinc amalgam was placed in the bottom of the test-tube and covered 
to the depth of about 2 centims with moist zinc sulphate crystals. The paste of 
mercurous sulphate and zinc sulphate crystals placed on top of the crystals was made 
in the usual way by mixing moist crystals with pure washed Hg 2 S0 4 . The positive 
electrode consisted of a platinum wire flattened at one end, amalgamated, and 
inserted in the paste. The wire was protected by a small glass tube and reached to 
the top of the test-tube, where the glass was melted around the wire to form a 
mercury cup. The negative electrode was a platinum wire protected in a similar way 
and thrust into the amalgam while still warm before the cell was filled with the other 
ingredients. The cell was sealed by shoving a cork down the test-tube, with the 
two electrodes passing through holes made for them, to within a few millims. of 
the ingredients. The cork was about 1 centim. thick, and was sealed by inserting 
particles of marine glue and melting them in place by carefully warming the glass 
over the cork. The crystals of zinc sulphate were prepared by re-crystallizing the 
ordinary pure heptahydrate salt after neutralization with zinc oxide, and treating 
with a small quantity of the washed Hg„S0 4 when in solution in the usual way. 
The cells made in 1898-99 were of the older type, with an amalgamated zinc rod 
with positive electrode at the bottom of the test-tube. They differed from the 
original crystal cells in having an amalgamated flattened platinum wire in place of 
