32 JoLty—On the Conservation of Mass. 
upon such a mass should in the absence of all frictional or other restraints produce 
the observed velocity. It follows that the force 0:0392 —0:0288 = 0:0104 dynes is 
expended in doing work in overcoming frictional resistance, and is doubtless, in 
small part, stored up in elastic potential in the suspending wire. This experiment 
is very instructive as to the sensibility of the arrangement. It may safely be said 
that the effect of the force of just 0°04 dynes for the interval of 30 seconds is 
perfectly distinctive, and could not be mistaken for any of the usual perturbations 
to which the beam is subject, arising from air-convection. Undoubtedly a still 
less force acting for this period would be distinctive; but as this force has been 
directly shown to be so in repeated experiments with the magnets, it is more 
satisfactory to accept this as the sensibility of the apparatus, just as we define the 
sensibility of a balance by a fraction above that which can be attained. We 
assume, then, that a force of 0:04 dynes acting for 30 seconds cannot in a series of 
experiments be confounded with the perturbation to which the measurements are 
subject. 
It remains to estimate what fraction of the force that might be expected this 
distinctive force represents. The dimensions upon which the more recent experi- 
ments have been carried on may be exemplified by the experiments on the 
solution of copper sulphate in water acidulated with sulphuric acid. Now 
Heydweiller’s quantities (Joe. cit., p. 410) are about 50 grms. of the salt, 150 grms. 
of water, and 7 grms. of sulphuric acid. ‘This will leave a residue of undissolved 
salt. Hence the quantity of liquid defines the amount of the reaction. I take 
from 25 to 380 grms. of the salt, and the same weight of water which has been 
acidulated in the proportions adopted by Heydweiller. The object of varying the 
proportions of solid and liquid is to secure the saturation of the latter under 
conditions where stirring cannot be resorted to, and rapid solution is essential. 
In fact, an excess of copper sulphate is used solely in order to provide increased 
surface. In the proportions used, the solid being brought to a very fine powder 
by prolonged grinding in an agate mortar, the liquid on its descent to the lower 
vessel is, as it were, entirely immersed, or nearly so, in the salt, if the expression 
is permissible. The rate of solution may be assumed to be almost as fast as the 
commingling of liquid and solid. Now it was found that it required from 25 to 
30 seconds for the transport of the liquid from the upper vessel to the lower. We 
take it, therefore, that in 80 seconds 25 grammes of the acidulated water becomes 
saturated. This is just one-sixth of the quantity used by Heydweiller. Now it 
was calculated above that, assuming Heydweiller’s weight-loss as 0-1 mgr. in 200 
grammes, and that this is effected in 60 seconds, a force of 2°54 dynes would act 
according to the equation for the change of velocity: 
mv 
