1866. | Physics, 599 
Professor Bunsen, which appears in the September number of the 
* Philosophical Magazine.’ 
Hxrar.—According to some experiments made by M. Gripon on 
the conducting power of Mercury for heat, it appears that if the 
conducting power of silver = 100 that of mercury = 3°54. It 
stands therefore the last of the metals, and a little before marble or 
gas coke. The author mentions that in this case the conducting 
power for heat and for electricity is very different, the former 
being 3°54, and the latter 1°80. 
Although scarcely coming under the heading of “ Heat,” yet as 
they point to a possible means of storing up heat and force for future 
use, we give here an abstract of Professor Graham’s most remarkable 
discovery in dialysis. The Professor finds that atmospheric air 
drawn through films of caoutchouc leaves behind a large portion of 
its nitrogen. The septum has no porosity, and is really impervious 
to air as gas; but the india-rubber film is capable of liquifying the 
individual gases of which the air is composed, whilst the oxygen 
and nitrogen, in the liquid form, penetrate the substance of the 
membrane wnequally, and appear on the other side, where they again 
become gaseous. The rubber film thus becomes a dialytic sieve for 
atmospheric air, and allows very constantly 41:6 per cent. of oxygen 
to pass through instead of the 21 per cent. usually present in air. 
This dialysed air rekindles wood burning without flame, and in 
many other respects can replace pure oxygen for laboratory and 
technical purposes. 
Exzcrrictry.—The electro-chemical properties of Magnesium 
have been applied to a very useful purpose by M. Roussin. Hitherto, 
in the toxicological examinations for metals, zinc has been exclusively 
employed, but this metal, as met with in commerce, is always impure, 
and the employment of magnesium has now been proposed as a 
substitute. Magnesium has the double advantage of rapidly and 
completely precipitating poisonous metals, without the danger of 
introducing any other poisonous substance. Arsenic and antimony 
are not precipitated, but will be found in the gas disengaged and in 
the liquid remainmg. The author destroys organic matter by the 
usual methods, concentrates the acid liquor, and then introduces 
ribbons of magnesium as long as any deposit is formed. This pre- 
cipitate is washed and examined by the usual method for metals. 
If the operation be conducted in a Marsh’s apparatus, the gases may 
at the same time be examined for arsenic and antimony. ‘The 
magnesium now to be purchased, in the form of ribbon or wire, is 
almost perfectly pure, and its price is so moderate that this can be 
no hindrance to its general use in laboratories. 
Some new electric batteries have been described by M. Mouthier. 
