Molecular Actions of Crystalline Particles, Sfc. 101 



of sulphur is found to consist of solid globules, several of 

 which adhere together; when acted upon by a gentle sol- 

 vent, their external portion is dissolved, and there remains a 

 regular octahedron. An interesting experiment may be made 

 on the fumes of sal-ammoniac, which appear whenever mu- 

 riatic acid and ammonia are brought together. Two small 

 phials, each containing one of these substances, are covered 

 by an inverted tumbler: above the surface of the acid are 

 seen at a short distance the fumes of the salt, which at the 

 end of a few hours are found to have condensed into a thin 

 snowy pellicle, completely obturating the mouth of the bottle. 

 This partition is so delicate, that the slightest agitation will 

 cause it to fall into the liquid. 



In all these cases it is found that the fumes possess the 

 power of remaining suspended a much greater length of time 

 than would be expected from the difference of their specific 

 gravity with that of air, which is also the case with the fumes 

 of other substances, and smoke in particular. This can only 

 be accounted for by the continual state of agitation of the air, 

 even within an enclosed space, and by the elasticity of the 

 solid and liquid particles. In the case of solid particles this 

 can be readily admitted, but with regard to liquid globules, 

 there is probably some action similar to that which takes place 

 on the impinging of solid elastic balls, which after becoming 

 flattened rebound in virtue of their tendency to recover their 

 original shape. 



The causes which act in fixing different vapours and fumes 

 are the same as those which determine the precipitation of solid 

 particles in solution, such as for instance, sharp points of any 

 kind, minute filaments, and more especially the existence of a 

 crystalline particle to act as a nucleus. Non-conducting sub- 

 stances, as woollen cloth, the nap of a hat, the web of the spider, 

 &c, are covered with aqueous globules when no rain has fallen, 

 and when polished surfaces near present no such deposition. 



Having now shown the existence of a crystalline power in 

 vapours, we shall proceed to prove the influence of a force 

 which disturbs this equilibrium in the same manner as in the 

 saline solutions above mentioned. The friction of a solid body 

 on glass will leave traces which are invisible until breathed 

 upon. 



are added to those of physiology. This tendency of the mind, of which 

 a good account has been given by Miiller in his Elements of Physiology, 

 is so strong, that where groups of globules are concerned, I would 

 always advise their being mapped down under the microscopic camera 

 lucida, and put by for some time for future inspection. I shall have 

 occasion to advert to this subject more fully hereafter. 



