xxxii Historical Sketch of the Physical Sciences, 1818. 
Berzelius, that it is a compound of one atom selenium and one 
atom hydrogen, or by weight of 
Selenium. ....+s thge L2o.. Sead 
Hydrogen. ........ 0°125 a ctics eae 1 
These would be the weights nearly, if we were to go over 
Berzelius’s experiments and modify the results in order to make 
them correspond with the weight of an atom of silver, oxygen, 
and hydrogen, as | have established these weights in a preceding 
volume of the Annals of Philosophy. 
Selenium combines with sulphur, phosphorus, and with all the 
metals tried. The phenomena, which take place during the 
formation of these selenurets are analogous to those which are 
exhibited by sulphur when it unites with the metals. For a 
particular account of the few facts ascertained by Berzclius 
respecting these selenurets, I refer to the paper of that indefa- 
tigable chemist in the last number of the Annals of Philosophy. 
Selenium, like sulphur, combines likewise with ammonia, with 
the fixed alkalies, and the alkaline earths. There is a striking 
analogy between the selenurets and sulphurets of these bases. 
6. Protoxide of Azote.—I may notice here that Mr. Faraday 
has pointed out the reason why the respiration of this gas some- 
times produces alarming effects upon the health of the person 
who employs it (Institution Journal, vi. 360). These effects are 
owing to the mixture of sal ammoniac with the nitrate of ammo- 
nia, from which the gas was procured. When such an mpure 
salt is employed, the sal ammoniac is decomposed in the nrst 
place, and there are evolved azotic gas, chlorine, &c. which are 
mixed with the protoxide of azote, and occasion the injurious 
effects. 
I must observe that these facts were pointed out many years 
ago in a paper published by Proust. He ascertained that the 
presence of sal ammoniac injured the protoxide of azote. He 
assures us that the first portions of gas driven off from such a 
mixed salt are of a peculiar nature. This assertion has not 
hitherto been verified, nor so far as‘I know even examined. 
7. Sulphuretted Azote.—It seems hardly necessary to notice 
the statement of Dr. Granville, that a gas composed of sulphur 
and azote is sometimes found in the abdomen in peculiar circum- 
stances. I have related in a former historical sketch, givenina 
preceding volume of the Annals of Philosophy, the discussions 
respecting this supposed compound which took place in Germany, 
and the unsuccessful experiments of Berzelius and others, who 
endeavoured to form it, or to obtain some evidence of its exist- 
ence. A compound of 10 sulphur + 891 azote would consist 
of one atom of sulphur united to about 9°7 atoms azote—a very 
unlikely compound indeed, and unlike that of any gas containing 
hydrogen with which we are acquainted. I have no doubt that 
what Dr. Granville took for sulphuretted azote was a mixture of 
E. 
