rf 
82 Dr. Thomson's Account of the [Fres- 
electrical powers of this and several other similarly endowed 
fishes, and have quite thrown into the shade the few facts com- 
municated by Dr. Ingenhousz in this paper. 
2. Easy Methods of measuring the Diminution of Bulk taking 
place on the Mixture of Common and Nitrous Air ; with Experi- 
ments on Platina. Phil. Trans. 1776, p. 257.—Dr. Ingenhousz 
employed Fontana’s eudiometer in his experiments on the dimi- 
nution produced by mixing common air and nitrous gas; and he 
describes in this paper several ingenious methods which he had 
recourse to in order to determine. more accurately the bulk of 
the two gases before mixture. But though Dr. Ingenhousz 
appears to have bestowed great attention upon this mode of 
determining the purity of air, and though he continued his 
experiments for a long series of years, chemistry derived very 
little advantage from the result of his researches. His notion of 
the nature and constitution, both of common air and nitrous 
gas, was inaccurate, and of course his opinion of the cause of 
the diminution of bulk which takes place when they are mixed 
was equally erroneous. Besides, he was not aware of the many 
circumstances which produce variations in the condensation 
even when the state of the two gases before mixture is precisely 
the same. The first person that pointed out the method of 
making this experiment with the requisite accuracy was Mr 
Cavendish, in a paper on a New Eudiometer, published in the 
Phil. Trans. for 1783. He showed in that paper that the purity 
of common air does not vary at different seasons of the year, and 
in different places, as had been previously supposed ; but that 
when the experiment is correctly made, we find its purity, or 
the proportion of its constituents, always exactly the same. It 
further appears from Mr. Cavendish’s experiments, that when 
common air is let up into nitrous gas, bubble by bubble, agitating 
the nitrous gas, during the whole time, over water, that oxygen. 
combines with, and condenses almost exactly, four times its 
volume of nitrous gas. Much pains have been taken by some 
of the most ingenious chemists of the present day, particularly 
by Mr. Dalton and M. Gay-Lussac, to determine how much 
nitrous gas is capable of uniting with oxygen gas. But I con- 
sider Mr. Cavendish’s determination of the maximum of nitrous 
gas as fully as accurate as any of the subsequent experiments. 
it seems to be nearly agreed upon that the mimimum proportion 
of nitrous gas is one yolume of oxygen gas and 12 of nitrous 
ae This proportion was first, I believe, hit upon by Sir. H. 
avy. 
Dr. Ingenhousz’s observations on platina are of little value. 
He found the grains of native platina attracted by the magnet- 
He could not melt them; but on passing an electric shock 
through a parcel of these grains put into a small glass tube, he 
cemented them together. We now know that the magnetical 
properties of the grains of platina are owing to the presence of 
