490 



EEPOET — 1882. 



experiments which he had made, conjointly with Professor Behrens of Delft, on its 

 application to chemical and mineralogical researches. He exhibited carbon bores 

 contained in iron handles, the mineral being fixed by an eqnal mixture of wax and 

 colophonium. These handles are fixed in a turning' machine, and thus the hardest 

 minerals can be operated upon as easily as iron by steel. For purposes of chemical 

 analysis this process of obtaining a powder is better than the use of mortars of 

 agate, porcelain, or steel, as the powder has no admixture of particles worn away 

 from the mortar. One great difficulty, however, is that of gi\ing any desired shape 

 to the carbon, owing to its extreme hardness. This difficulty tlie author had over- 

 come as follows : — A piece of carbon is wholly covered by a thin layer of pipeclay 

 like that used in making tobacco-pipes ; after this has dried the part covering the 

 portion of carbon to be removed is taken oft". The whole is then heated till the carbon 

 is white hot by the action of a Bunsen flame under a blowpipe, then a stream of 

 oxygen is directed on the carbon through a thin platinum tube until the desired 

 portion is removed by combustion. The carbon is then plunged in oil. Specimens 

 which had been thus acted upon were exhibited. 



4. On the Action of the Component Salts as Nuclei on Supersaturated 

 Solutions of certain Compound Salts. By John M. Thomson, F.C.S. 



In a paper published in the Chemical Society's Journal, May, 1879, on ' The 

 Action of Isomorphous Salts, in producing the Crystallisation of Supersaturated 

 Saline Solutions,' the author pointed out that if a mixture of dimorphous salts be 

 taken, a separation of the salts may be effected within certain limits by touching the 

 solution with a crystal of one or other of the salts ; this separation being limited 

 by and depending on the relative solubilities of the different salts contained in 

 the solution. 



The subject of the present paper is a continuation of these observations, 

 employing in |this case supersaturated solutions of double salts, where it was 

 possible to obtain such, and acting on them with nuclei consisting of one or other 

 of the component salts in order to find whether any disruption of the compound 

 takes place by the action of tlie nucleus. The method of carrying out the experi- 

 ments was exactly the same as that employed before, and fully described in his 

 first paper, the nucleus being added to the solution to be experimented on by one 

 of two methods: (1) by the nucleus being obtained by crystallisatio)i from a 

 supersaturated solution, and in this condition retained in the syphon-tube in the 

 neck of the flask till required for use ; or (2) the nucleus being added directly 

 from its mother-liquor in a bulb-tube suspended in a similar manner in the neck 

 of the flask. 



In all these experiments, as before, the substances were purified with the 

 greatest care, and the admission of particles from the external air most carefully 

 guarded against. 



The following tables give the results obtained with the different groups of salts 

 employed. 



