212 Dr. Playfair oh Transformations 



zers, just as a ball of spongy platinum silently effects the 

 union of these two gases. 



In these cases we must admit that the action is indepen- 

 dent of a state of intestine motion of the atoms of one com- 

 pound molecule imparted to those of another, or, if we do not 

 allow this, we must create two new powers and separate de- 

 compositions caused by inorganic bodies from those produced 

 by organic compounds, although all the phaenomena of the 

 decomposition show them to belong to one category. 



In a body in a state of such incessant change as the blood 

 of living animals, it would naturally be expected that an added 

 agency, such as that described, would render it prone to 

 abnormal actions and oxidations, and in fact we do recognise 

 by all the recent progress in the study of public hygeine 

 that the addition of any oxidizing miasm or putrid matter 

 to the blood does produce those changes which are known 

 by their results in the different forms of disease. These and 

 other catalytic agents no doubt exercise most important in- 

 fluence on the processes of animal life and on the action of 

 medicaments on the system, but it would be foreign to the 

 object of this paper to examine them in detail. 



The limits of a paper such as this compel me to avoid 

 including many other instances of catalytic decompositions 

 which come under this explanation, or of drawing special 

 attention to those which cannot be included in the present 

 state of our knowledge. Thus diastase, acting on starch, 

 converts it into sugar, but we have so little knowledge of 

 the composition or properties of the first body, that it would 

 be unwarrantable to embrace a case such as this. But 

 in analogous changes produced by bodies which are under- 

 stood, the same power is recognised. Sulphuric acid in 

 converting starch into grape-sugar offers an example of 

 combination Avhich may fairly be examined by the same 

 method employed in investigating other decompositions. 

 Graham has shown* that heat is evolved even on the addi- 

 tion of the 48th atomic proportion of water to sulphuric acid, 

 or, in other words, that the affinity of that acid for water is 

 not gratified as long as our instruments of research can follow 

 the change. This is merely another proof of the doctrine 

 with which I started, that there is no evidence of such a 

 complete gratification of affinity as ever to merge entirely the 

 attractions of the elements of any body. In the case referred 

 to, the development of heat on each successive addition 

 proves that the water is condensed on entering into union 

 with the acid. When the heat of the sulphuric acid is arti- 

 * Phil. Mag. Third Series, vol. xxii. j). 334. 



