Major-Gen. MacMaJwn—Nature\ Manufacture of Serpentine. 75 



Fi'om Professor Blake's insertion of " \_sic] " after atoms, I infer 

 that he regards a molecule as a homogeneous, solid body like a 

 bullet, as it appears to our unaided vision ; if so, his conception 

 of the constitution of a molecule can hardly be considered " up 

 to date," as the following brief extracts from two well-known 

 works will show. "Atoms cannot be divided physically; they are 

 retained side by side, without touching each other, being separated 

 by distances which are great in comparison with their supposed 

 dimensions. A group of two or more atoms forms a molecule." ' 

 " Nor should it be forgotten that, granting the fundamental hypo- 

 thesis of the molecular and atomic theory, and also granting that 

 each atom can directly interact with a limited number of atoms 

 in a molecule, we are obliged to regard the atoms which form any 

 molecule as performing constant regulated movements, and not as 

 might be supposed by a careless or superficial reader of the atomic 

 explanation of isomerism, as in absolutely fixed positions within the 

 molecule." ^ 



According to modern conceptions, therefore, the atoms which 

 constitute a molecule are linked together, but the linking is analo- 

 gous to that of moons to a planet, and of a planet and its moons to 

 the sun. 



The illustration which Prof. Blake adduces, at the end of the 

 above extract, in support of his objection, seems to indicate a 

 fundamental misapprehension on his part. The case of the hydrate 

 of sodium sulphate seems to me to have no bearing on the point at 

 issue. In my paper I discuss the mode in which the hydration of 

 a specified silicate is brought about in a rock below the surface of 

 the earth in the presence of water under considerable pressure ; and 

 Prof. Blake opposes the case of the dehydration of a salt by heat 

 under ordinary atmospheric pressure at the surface of the earth, 

 and in the absence of water. There seems to me to be no analogy 

 between the two cases. We all know that at the surface of the 

 earth calcium carbonate can be converted into lime (CaO) by raising 

 its temperature to a certain point; because at that critical tempera- 

 ture, the force of repulsion, generated by the heat, overcomes the force 

 of the attraction between the calcium oxide and the carbon dioxide, 

 and the latter passes into the gaseous state. Under plutonic con- 

 ditions, on the other hand, the carbon dioxide remains in union with 

 calcium oxide, and crystalline calcite is formed. 



In my paper I was considering the question of capillary flow 

 under heat and pressure. I showed that, " although the pressure 

 under which water is put in circuluation through the capillary pores 

 depends on the head" (" 43 lbs. per square inch per foot in height"), 

 "the freedom with which this water flows through the capillaries" 

 must, with reference to the experiments of Poiseulle, be increased 

 by heat. I contended, therefore, that if " the pressure under which 

 water is being injected into the pores of a mineral remained 

 constant, heat would facilitate the capillary flow through those pores 



^ Ganot's Elements of Physics, by Atkinson, p. 1. 



■^ Principles of Chemistry, by Patteson Muir, p. 154, footnote. 



