System of Chemical Notation. 135 



chlorine), and H 2 , H 2 0, H 2 O 2 (hydrogen, water, peroxide of 

 hydrogen), which the author now gives us on the basis of hypo- 

 thesis. But if hydrogen were proved to be compound, a very 

 large number of the author's formulae would require to be essen- 

 tially changed, and the meaning and weight of many of the 

 prime factors would be affected. If, for instance, hydrogen 

 were decomposed into two simpler substances, so that ot=7)7r 2 , 

 chlorine would become 17^ 2 instead of «^ 2 , and % 2 would not have 

 the same weight as %. The same change would require to be 

 made on the symbols of all the elements of the form «/x 2 . From 

 this we see that the stability of the present system is greater 

 than that of the system proposed. 



3. The present formulae express the composition of substances 

 as far as that is known to us. Thus when we see C or H in a 

 formula, we know that the substance represented will give us 

 carbonic acid or water if subjected to suitable methods of oxida- 

 tion ; and we also know from the formula how much of each it 

 will yield. When we see k in a symbol, we also know that the 

 corresponding substance will yield carbonic acid, but the presence 

 of a does not, without an arithmetical operation, give us any 

 information as to whether water can be obtained. 



Another disadvantage of the new symbols is that, however 

 carefully their author may guard against such a misconception, 

 the symbols a^ 2 , av 2 , &c. will certainly be interpreted as mean- 

 ing that chlorine, nitrogen, &c. contain hydrogen in the same 

 sense as peroxide of hydrogen, af 2 , does. It may be that they 

 do j but it is surely well to make a sharper distinction than this 

 between observed fact and speculation. To show that this is 

 not an imaginary danger, I need only observe that the author 

 himself refers to water, af, and to hydrochloric acid, a%, as simi- 

 larly composed " by two indivisible operations." The two ope- 

 rations referred to are obviously a and f in the case of water, 

 and a and^ in the case of hydrochloric acid, Now a is the ad- 

 dition to a litre of space of a litre of hydrogen, and is an operation 

 which may be regarded as one of the steps in the formation of a 

 unit of water. It is^ however, by no means proved that it is a 

 step in the formation of a unit of hydrochloric acid ; if a litre of 

 hydrochloric acid does really contain a litre of hydrogen (and 

 that remains to be proved), the hydrogen has not been put there 

 by one indivisible operation, but by two. Further, f and % are 

 purely imaginary operations, f being the addition to a litre of 

 space of a litre of an imaginary oxygen having half the density 

 of the gas known by that name, and % the similar addition of 

 an unknown component of chlorine. 1 see no objection to the 

 assumption of imaginary substances or operations ; but a system 

 which abounds in them and does not carefully distinguish them 



