148 Notices respecting New Books. 
rooms which are most suitable for gas laboratories. The jar is 
therefore best charged by means of the simple and effectual arrange- 
ment represented in fig. 32. 
‘It consists merely of a large porcelain tube, which, when held 
before the iron wire of the cylinder and rubbed with silk and amal- 
gam*, evolves so much electricity that the jar is charged in a few 
seconds.” 
One great advantage of Bunsen’s mode of treating the subjects is, 
that he illustrates by numerous examples, and enters fully into the 
best aud shortest modes of calculating the results. 
A considerable portion of the volume is devoted to the description 
of the methods required to meet special cases of gaseous analysis, the 
whole being copiously illustrated by examples, and even the most 
minute precautions being detailed. 
Much new and interesting matter of the highest value is contained 
in the portion treating of the ‘‘ manipulation in the absorption of 
gases ;’’ and having described the order of the processes, the author 
proceeds to develope a general formula, enabling the operator to cal- 
culate the relative volumes of the constituents of a mixture of known 
gases. 
The chapter on the specific gravities of gases strongly shows the 
neatness and ingenuity of the author as an operator. This is well 
seen in his illustration of the determination of the density of gaseous 
bromide of methyle, made with a flask of only 44 cubic centimetres 
capacity. Notwithstanding the small volume, the experiment gave 
3°253, theory requiring 3°224. 
In addition to methods involving the necessity for weighings, he 
uses effusion as a mode of determining the densities of gases where 
only small quantities are at the operator’s disposal. The gas effuses 
through a minute aperture in a thin platinum plate attached to an 
apparatus resembling an inverted Mohr’s burette with a glass stop- 
cock. The observations of time are made with a pendulum vibrating 
half-seconds. ‘The contrivance by means of which the times of effu- 
sion of the gases are determined, and warning is given of the ap- 
proach of the termination of the experiment, is both simple and in- 
genious. In fact, when we couple the simplicity of the mode of 
operating with the fact that an experiment can be made on so small 
a quantity of gas as two cubic inches, it is scarcely too much to say 
that in many researches it will entirely do away with the necessity 
of weighings. 
* «The amalgam, by the aid of which a porcelain tube 3 feet long and 14 
inch thick may be made to supply the place of a tolerably powerful elec- 
trical machine, is made as follows :—Two parts of mercury are heated in a 
common test-tube, and one part of thin zinc-foil, and one part of zine added 
whilst the metal is well stirred. In order to make the amalgam more 
plastic, it is melted and stirred several times, and then placed in a piece of 
the thickest and best silk, which serves as a rubber. In rubbing the tube, 
the silk is so arranged that only half the surface in contact with the porce- 
Jain is covered with amalgam, the remainder being left free. The powerful 
action of the amalgam begins generally after it has been some time in use, 
and it preserves its activity often for months.” 
