Chemical Science. 379 
dipped into ammonio-muriate, or muriate of platina, until about two 
grains are taken up, after which it is to be heated red-hot in a spirit 
lamp. In this way a quantity of spongy platina is formed on the 
wire so minute, that if put into contact with a mixture of oxygen 
and hydrogen it becomes heated, and inflames the gas as rapidly 
almost as if an electrical spark had passed. Such a wire as this 
fixed on the jet-pipe, so that the spongy metal shall be exposed to 
the current of hydrogen, immediately inflames it. It happens that 
if an instrument of this kind has been exposed for some hours to a 
humid atmosphere, the inflammation does not take place readily, but 
in this case if the top of the platina be touched by the finger or palm 
of the hand, either before or during the time that the current of hy-= 
drogen is passing out, the inflammation immediately takes place. 
Contact, indeed, is not necessary, for the mere approach of the hand 
is sufficient to elevate the temperature so much as to cause instant 
inflammation. 
In using spongy platina for eudiometrical purposes *, M. Dobe- 
reiner attaches his balls to the end of a platina wire, so as to be able 
to withdraw them when the experiment is completed, or even during 
the experiment if requisite, so that they may be dried and again 
introduced.—Bib. Univ. xxv. 117. 
10. Test of the Alteration of Soiutions by contact with Air.— 
M. Becquerel remarks, that if iron be dissolved in nitric acid, and 
the solution filtered, and two plates of platina connected with the 
two extremities of the wire of a galvanoscope, be immersed into 
the solution, and if one plate be withdrawn, and then re-introduced 
into the solution, it will produce an electric current passing from 
this plate to the other; and generally the plate withdrawn from the 
solution and re-introduced becomes positively electrical. 
The nitrates of copper and lead give similar results, but they do 
not retain this power, and in the course of a few hours no effects of 
this kind are observable. Nitrate of zinc does not operate in this 
manner. Suspecting that the effect was due to the action of air on 
the film of solution which adheres to the withdrawn plate, the expe- 
riment was made in an atmosphere of hydrogen, and then no such 
results were obtained. M. Becquerel, therefore, attributes the effec t 
to the alteration induced by the air on the portion of solution with- 
drawn with the plate, and which, when the plate is re-immersed, 
being dissimilar to the fluid that has not been exposed, determines 
the current of electricity, The effect of the air he considers is pro= 
bably to convert such portion of deutoxide of azote and proto-nitrate 
as may have been formed by the action of nitric acid on the metal 
into nitrous acid and deuto-nitrate, and that when this has taken place 
* See Vol xvi. page 874. 
