SIE B. C. BEODIE ON THE CALCULTJS OF CHEMICAL OPEBATIONS. 



815 



The chief arguments by which this view is supported are derived from the observations 

 (1) that it is very rarely that the indices of the prime factors of chemical symbols have 

 a common measure ; (2) that on this assumption the symbols of hydrogen, water, and per- 

 oxide of hydrogen constitute a series of the form a, a^, a|^ ; and that the densities of 

 these substances form an arithmetical progression, being 1, 9, 17 ; and that such series 

 so frequently occur in the actual system of chemical symbols as to render probable their 

 existence in the future system. 



The conclusions at which we thus arrive are not to be regarded as necessarily final. 

 Not only is it possible that further information as to the chemical properties of the per- 

 oxide of hydrogen might lead us to the adoption of a more complex symbol, but we can 

 even specify the very facts, the discovery of which would induce us to modify our opinion. 

 But, nevertheless, the choice of the expression a^- as the symbol of the unit of this sub- 

 stance is not an arbitrary and conventional selection. It expresses the most probable 

 opinion which, with our actual knowledge, we can form as to the nature of the equation 

 from which it is derived, and which we provisionally embody in the symbol for the pur- 

 pose of tracing the consequences of our hypothesis. 



The weight of that portion of any chemical substance which I have termed the che- 

 mical unit of ponderable matter, is (Sec. I. Def. (10)) the weight of that portion of each 

 substance which in the gaseous condition, at 0° C. and 760 millims. pressure, occupies 

 the space of 1000 cub. centims. This weight may be measured in two ways ; either by 

 comparison with the weight of a cubic centimetre of distilled water at 4° C, or by com- 

 paring it with the weight of the chemical unit of hydrogen. We shall hence have two 

 series of numbers by which the weights of the portions of ponderable matter resulting 

 from any chemical operation are expressed, viz. 



1. The absolute weight in grammes. 



2. The relative weight or density as compared with the weight of the xmit of hydrogen. 

 This second series of numbers may also be regarded as expressing the absolute weight 

 of the units of ponderable matter as estimated in "criths"*. 



Combinations of the Prime Factors a and 5. 



* HoFMANS, he. at. (Sec. I. (11)). 



t In calculating the absolute weight, it is necessary to assume the absolute weight of the gaseous litre at 0° 

 and 760 millims. pressure, of some one substance as accurately determined. The weight of a litre of oxygen is 

 here assumed as the standard, and the other numbers are calculated from it. 



5s2 



