xxx Historical Sketch of the Physical Sciences, 1818. 
shall have it in our power to determine the quantity of oxygen 
which united with the selenium and served to acidify it. One 
part of selenium, when converted into a chloride, was found to 
weigh 2°79 parts. This chloride being dissolved in water, and 
precipitated by nitrate of silver, the precipitate was washed with 
boiling water, acidulated with nitric acid, till all the seleniate of 
silver at first precipitated was redissolved. The residual chloride 
of silver was dried and fused. It weighed 7:2285. Now chlo+ 
ride of silver is a compound of one atom silver = 13°75 + 1 
atom chlorine = 4:5. Of course the quantity of chlorine im 
7:2285 of chloride of silver must be 1:782. To convert this 
chlorine into muriatic acid, we must combine. it with 0:0495 of 
hydrogen. Now as the weight of the oxygen in water is eight 
times as great as that of the hydrogen, it is evident that if we 
multiply 0:0495 by 8, we shall have the weight of oxygen that 
is requisite to convert one of selenium into selenic acid. But 
0:0495 x 8 = 0°38. Hence it follows, if the experiment was 
accurately made, that selenic acid is a compound of 
Neleuiuns Jos arate wia cee ote: 1 kOe 
APR OCT. tanam eerenees tee ae ot Cet 
138 
The constituents of the acid, as deduced by Berzelius from the 
preceding experiment, are, 
Seleniviin fF & 28 82 PES 100-00 
Oxyven..... pee WEES Na tea 40°33 
His mode of reasoning was quite different from that which I 
have followed; but the difference in our results is owing to small 
differences in our notions respecting the constitution of chloride 
of silver. I see no reason for doubting that the weight which I 
have assigned to an atom of silver; namely, 13°75, is the true 
weight. Berzelius’s number is equivalent to 13-44. Hence the 
quantity of chlorine in chloride of silver is a little more than I 
make it; and from this arises the difference in the weight of our 
oxygen. 
If we suppose the chloride of selenium formed by Berzelius to 
be a compound of two atoms of chlorine and one atom of sele- 
nium, as is most likely, then we have 1°79 : | :: 2°56 : 2°514, and 
2:514 x 2 = 5-028 will be the weight of an atom of selenium, 
The weight of an atom of selenium derived from the notion that 
selenic acid is a compound of one atom selenium and two atoms 
oxygen will be 5°263; but the first estimate is probably most 
accurate. In the present state of our knowledge, we might 
reckon 5 as the weight of an atom of selenium. 
On this supposition, which cannot be very far from the truth, 
an atom of selenic acid will weigh 7. Now this corresponds 
pretty well with the constitution of the only two seleniates of 
