4 2o SCIENCE PROGRESS. 



we are wholly ignorant of the cause of chemical change. 

 All we can say is that it obeys the fundamental laws of 

 energetics, and we know that as our knowledge of the 

 special characteristics of chemical energy increases we shall 

 be able to correlate it more closely with the other forms of 

 energy, and thus in some measure arrive at an explanation 

 of the occurrence of chemical phenomena. 



A problem much better adapted to the state of science 

 to-day is the investigation, not of the ultimate nature of 

 chemical affinity, but of its magnitude. This problem was 

 clearly before many chemists at the beginning of this 

 century, and they arrived at ideas on the subject which are 

 not yet out of date, and can bear repetition. Nicholson, in 

 his Dictionary of Chemistry (1808), gives the following 

 account of Berthollet's views (article, " Attraction ") : — 



" Mr. Berthollet has lately made a great number of 

 experiments, from which he deduces the following anomaly : 

 that in elective attractions the power exerted is not in the 

 ratio of the affinity simply, but in a ratio compounded of 

 the force of the affinity and the quantity of the agent ; so 

 that quantity may compensate for weaker affinity. Thus 

 an acid which has a weaker affinity than another for a 

 given base, if it be employed in a certain quantity, is 

 capable of taking part of that base from the acid that has a 

 stronger affinity for it ; so that the base will be divided 

 between them in the compound ratio of their affinity and 

 their quantity. This division of one substance between 

 two others, for which it has different affinities, always takes 

 place, according to him, when three such are present under 

 circumstances in which they can mutually act on each other. 

 And hence it is that the force of affinity acts most power- 

 fully when two substances first come into contact, and 

 continues to decrease in power as either approaches the 

 point of saturation. For the same reason it is so difficult 

 to separate the last portions of any substance adhering to 

 another. Hence, if the doctrine laid down by Mr. Berthollet 

 be true to its utmost extent, it must be impossible ever to 

 free a compound completely from any one of its constituent 

 parts by the agency of elective attraction. . . . 



