418 
LIR. E. H. GRIFFITHS ON THE VALUE OF 
except that every withdrawal involved four weighings, so that, after a short time, 
the mass of water in the calorimeter was dependent upon a very great number of 
weighings, and small errors in each, if cumulative, might have become serious. We. 
therefore, soon abandoned this as a general method, and only resorted to it occa¬ 
sionally. Since then we have always used the following method of adding a known 
mass of water to the calorimeter :— 
Pairs of glass flasks (with india-rubber stoppers), of 100, 200, and 300 cub. centims. 
capacity, were selected and carefully cleaned. One of each pair was kept as a tare 
for its fellow. In introducing the water into the calorimeter it was necessary to avoid 
loss either by accident or by evaporation, and to guard against losses of this kind the 
following device was employed :—A thin glass tube, 30 centims. in length, had a 
wider piece, about 7 centims. long and 2 centims. in diameter, fused to its upper 
end, thus forming a funnel. Up the centre of this wide portion a piece of glass rod 
was fixed, its upper extremity projecting above the top of the wider tube, so that the 
lip of the flask, from which water was poured, could rest against it, and thus prevent 
any drops running down the outside of the flask or tube. By forming a slight 
support, it also somewhat relieved the difficulty of the operation, which, even with 
its aid, was a trying one. A cork was fixed to the stem of the funnel, in such a 
manner as to permit its lower end to dip into the calorimeter. This funnel was 
provided with a case, consisting of a length of glass tube closed permanently at the 
lower, and temporarily at the upper, end by an india-rubber stopper. A piece of 
similar tubing, closed at both ends, was used as a tare. The full flask and funnel 
having been weighed, the funnel was withdrawn from its case, placed in one of the 
tubes leading to the calorimeter, and the water poured down it from the flask. This 
is the only part of the process during which evaporation could possibly take place, 
and any such loss, during the few seconds the operation lasted, would be a matter of 
no consequence. The empty flask was immediately re-stoppered, the funnel with¬ 
drawn and returned to its case, and the weight ascertained at any convenient time. 
This method also enabled us to. add water below the dew-point of the room without 
any error due to moisture condensed on the flask and funnel, for it was only necessary 
to first weigh the flask, then cool it, and pour its contents into the calorimeter. The 
exterior of the funnel was dried before returning it to its case, and the stoppered 
.flask idaced in a dessicator for some time before the final weiahino;. This method 
appeared to be satisfactory, and, although it was impossible to add exactly the same 
amount on different occasions, still, as the difference was only the fraction of a gramme, 
it was easy to apply any necessary correction to the resulting numbers. A glass 
tube, reaching to the bottom of the calorimeter, was connected with an exhaust pump, 
which enabled us to withdraw nearly all the water, and the remaining moisture was 
removed by passing a current of hot dry air through the calorimeter for several hours. 
Owing to some difficulty with regard to the air-tight joints, we were obliged to 
take the calorimeter to pieces at the beginning of July, 1892, and to our astonishment 
