Intelligence and Miscellaneous Articles. 399 
--The authors anticipate that admixture with a permanent gas may 
serve as akind of reagent to distinguish between cases of unusually 
high expansion-coefficient in a vapour, and cases where chemical 
alteration takes place. It will also be possible, by the employment 
of a permanent gas, to obtain vapour-densities of compounds which 
will not bear boiling without undergoing decomposition. 
In experimenting upon substances which may be heated above the 
boiling-point, the authors employ Gay-Lussac’s process for taking 
the specific gravity of vapours. A slight modification, however, is 
necessary. Previous to the introduction of the bulb containing the 
weighed substance, dry hydrogen is introduced into the graduated 
tube and measured with all the precautions belonging to a gas ana- 
lysis. It will be obvious that in the subsequent calculation the 
volume of hydrogen corrected at standard temperature and pressure 
must be subtracted from the volume of mixed gas and vapour, also 
corrected at standard temperature and pressure. 
_ When the substance will not bear heating to its boiling-point, the 
authors employ a process resembling that of Dumas in principle, but 
differing very widely from it in detail. Dumas’s flask with drawn- 
out neck is replaced by two bulbs, together of about 300 cub. cent. 
capacity, joined by a neck, and terminating on either side in a nar- 
row tube. Oneof the narrow tubes has some very small dilatations 
blown upon it (0), the other is merely bent (D). (See Plate V. fig. 6.) 
The apparatus, whose weight should not exceed 70 grms., is weighed 
in dry air, then placed in a bath, being secured by a retort-holder 
grasping the neck joining the large bulbs Cand C. The end A, 
projecting over the one side of the bath, is made to communicate 
with a hydrogen apparatus; the end D passes through a hole -in 
the opposite side of the bath, which is plugged up water-tight by 
means of putty. Dry hydrogen is transmitted through the whole 
arrangement, and escapes at D through a long narrow tube joined 
to it by a caoutchouc connecter. 
The bath is next filled with warm water until the bends a and a 
are covered. The connexion with the hydrogen apparatus is then for 
a moment interrupted, to allow of the introduction of a small quantity 
of the substance at A. The substance, which should not more than 
half-fill the small bulb 4, is partially vaporized in the stream of hydro- 
gen, and in that state passes into the part CC. All the while the 
temperature of the bath is kept uniform throughout by constant 
stirring, and .made to rise very slowly. When within a few degrees 
of the temperature at which ‘the determination is to be made, the 
current of hydrogen is almost. stopped, so that the bulbs C and C 
may contain less vapour than will fully saturate the gas at the tem- 
perature of sealing. The water of the bath is then made to subside, 
by opening a large tap placed near the bottom. The bends a and a 
are thus exposed, the bulbs CC remaining covered. Immediately 
the current of hydrogen has been stopped, the flame is applied at. 
aa, so as to seal the apparatus hermetically. The temperature of the 
bath, as well as the height of the barometer, must now be observed. 
