On the Use of Sulphate of Soda in the making of Glass. 379 
ef refraction, and d the density of the body, the refracting 
~ 
power _*—1 js not only variable for one and the same class of 
d 
rays, but also the law according to which this change is effected 
is different for the variously coloured rays. 
In the carburetted sulphur which we have already chosen for 
example, the ratio of the dispersive power to the refracting power 
is 0-14 in the liquid state, whereas it is reduced to 0°88 in the 
state of vapour. ; 
Thus, while the variation of the refracting power may be also 
accounted for, by admitting that the attraction of one and the . 
same body for light varies according to a law different from that 
of the direct ratio of the densities, we see that in order to give 
an account of the variation observed in the dispersive power, we 
must suppose besides that the action of a body on the various 
oloured rays follows in the changes of density a different law 
for each of those rays. These various suppositions diminish, 
without doubt, both the simplicity and the probability of the 
Newtonian theory ; but before deciding any thing in this respect, 
t is necessary, we repeat, to examine with great care the changes 
which the refracting powers of bodies undergo, either by 
ariations of density or by the effect of combination. It is in- 
ispensable also to join to these determinations such as are re- 
lative to the dispersive powers, to which experimentalists have 
ot hitherto paid any attention, and which, as we have already 
ounced, may by means of numerous precautions be deduced 
from direct experiments. 
Although the work which we purpose to publish on this sub- 
ject be very far advanced, we have thought it right to communi- 
sate beforehand the results furnished to us by our experiments on 
ids and vapours. , 
LXXVIL. On the Use of Sulphate of Soda in the making of 
Glass. Ly the late M. Genten*. 
. GruLEN, of whose valuable services chemistry has lately 
a deprived by a premature death, was much occupied with 
he manufacture of glass, and employed the sulphate of soda as 
flux. It is not the salt which is vitrified with the silex ; but 
her the soda, which abandons the sulphuric acid at a high 
temperature, on account of the chemical action which. soda and 
ilex exercise upon each other, After a great number of ex- 
* Translated from the Journal de Schweiger, vol. x¥. p. 89. 
periments, 
