6 Improvements in Physical Science [Jan. 
siderable number of these hydrurets. I forbear to give the details, 
because I do not perceive sufficient proofs that the substances de- 
scribed are hydrurets. 
4. In the Ann. de Chim. et Phys. ii. 59, there is a curious 
memoir by M. Dessaignes on the influence of éemperature on elec- 
tricity. He shows that heat and cold both alter the quantity and 
the kind of electricity. The facts are important, because they 
bring into view a new branch of electricity, which has hitherto been 
neglected. But they are of such a nature as not to be susceptible 
of abridgment. I shall, therefore, lay a translation of them before 
my readers ina future number of the Annals. 
5. In the Annals, viii. 74, there are two very curious galvanic 
experiments by Mr. Porret, which deserve the particular attention 
of physiologists and electricians. He found that when a galvanic 
battery has become inefficacious, it again recovers its energy by 
withdrawing the greater part of the liquid from the cells so as to 
uncover the plates of metal. He found that galvanic electricity has 
the property of forcing water through the coats of a bladder, so as 
to cause it to accumulate on the negative side in a vessel of water 
divided into two by a perpendicular diaphragm of bladder, 
VI. CHEMISTRY. 
This science, as usual, will occupy the greatest portion of our 
historical retrospect. We shall follow our former method of subdi- 
viding the facts which we have to detail, and of placing them 
under various heads, for the convenience of the reader. 
I, APPARATUS. 
Chemical experimenting has of late years been brought toa much 
greater precision than was formerly thought possible ; owing to the 
gradual improvement and simplification of the apparatus employed. 
Every amelioration, therefore, in any chemical instrament what- 
ever, deserves the attention of the practical chemist. On this ac- 
count I think it worth while to notice some improvements that have 
neen made known in London during the course of the preceding 
year. 
“ 1. Mr. Newman, of Lisle-street, so well known to chemists as 
an ingenious maker and improver of chemical instruments, has 
proposed the following mercurio-pneumatic apparatus, which pro- 
mises to be of considerable utility when experiments are to be made 
upon the gases rapidly absorbed by water, and which require, in 
consequence, to be confined over mercury. It consists in combining 
Mr. Pepys’s gasometer with the common mercurial trough, The 
engraving (Plate LX. Fig. 1) exhibits an outline of the apparatus 
as represented by Mr. Newman in the Journal of the Royal Insti- 
tution, i. 185. 
It requires about 70 lb. of mercury to fill it. The trough has a 
cavity in the middle large enough to fill a jar 10 inches long, and 
21 wide; and there is ashelf on each side, three inches in width, 
