856 Prof. H. E. Armstrowi oii^Lou'-Tem]ierature ResearcJt 



continuous proof of the accuracy of his contention : achievements such 

 as the production of the natural colouring matters (the madder colours, 

 indigo, etc.) by artificial means are entirely the outcome of the 

 command secured by chemists through their studies of the internal 

 structure of molecules and of function as determined by structure. 

 Yet it must be confessed that the doctrine of the small pores of 

 bodies is but beginning to attract the share of attention which is. 

 due to its importance, especially in relation to the properties of soils. 



Priestley, the pioneer investigator of different kinds of air, in the 

 third volume of his " Experiments and Observations relating to various 

 branches of Natural Philosophy," published in 1786, refers to "the 

 property that charcoal has of absorbing air" as "a remarkable 

 circumstance first observed by the Abbe Fontana, physicist to Duke 

 Ferdinand 11. of Tuscany " ; and he also speaks of having repeated 

 the Abbe Fontana's experiments by introducing hot charcoal through 

 mercury into vessels containing different kinds of air. Priestley, 

 indeed, seems to have been made acquainted with the power that 

 heated charcoal has of absorbing gases by Fontana himself in 1770. 



That the subject attracted attention at about the l^eginning of 

 last century is clear from a statement made by Dalton in his "New 

 System of Chemical Philosophy" (]>!1<), part ii. p. 235) : — 



" Several authors have maintained that charcoal after l)eing heated 

 red has the property of absorliing most species of elastic fluids in such 

 quantities as to exceed its bulk several times ; by which we are to under- 

 stand a chemical union of the elastic fluids with the charcoal. The 

 results of their experiments on this head are so vague and contradictory 

 as to leave little credit even to the fact of any such absorption. I made 

 1500 p'ains of charcoal red hot, then pulverised it and put it into a 

 Florence flask with a stopcock; to this a bladder filled with carbonic 

 acid was connected; this experiment was continued for a week and 

 occasionally examined by weighing the flask and its contents. At first 

 there appeared an increase of 6 or 7 grains from the acid mingling with 

 the common air in the flask of less specific gravity ; but the succeeding 

 increase was not more than 6 grains and arose from the moisture which 

 permeated the bladder : for the bladder continued as distended as at first 

 and finally upon examination was found to contain nothing but atmo- 

 spheric air. Yet carbonic acid is stated to be the most absorbed by 

 charcoal. One of the authors above alluded to asserts that the heat of 

 ])oiling water is sufficient to expel the lireater part of the gases so- 

 absorbed. Now this is certainly not true, as Allen and Pepys have 

 shown; and most practical chemists know that no air is to be obtained 

 from moist charcoal below red heat. Hence the weight acquired by fresh 

 made charcoal is in all probability to be wholly ascrilied to the moisture 

 which it absorbs from the atmosphere ; and it is to the decomposition of 

 this water and the union of its elements with charcoal that we obtain 

 such an abundance of gases by the application of a red heat."' 



In view of the crudeness of Dalton's methods, it is perhaps not. 



