1870.] On Furfur aniline and Furfurtoluidine. 537 



to form supersaturated solutions, and they become more sensitive to the 

 action of nuclei as the temperature falls, or, in other words, as they be- 

 come more highly supersaturated. Thus a very strong solution of calcic 

 chloride, which is not sensitive to nuclei at 40° or 45°, becomes very much 

 so at 24° to 34°. 



The sodio-zincic sulphate contains only 4 proportionals of water of 

 crystallization, and hence its supersaturated solutions are not stable at 

 low temperatures. When freshly made, they may be reduced to 10°Fahr. 

 withouts eparation of the salt ; but by repose, even in clean tubes and in 

 the absence of nuclei, long crystals of the separated salts occupy the 

 length of the tube, but they are invisible on account of having the same 

 refractive index as that of the solution in which they are immersed. In 

 the course of time, probably from the escape of vapour of water through, 

 the porous plug, they become visible. 



A solution of the ammonia zincic sulphate at 4° Fahr. formed beautiful 

 large feathery crystals of an opaque white, which gradually filled the tube. 

 They melted rapidly at 32°. 



A supersaturated solution of nickel sulphate resisted a temperature of 

 6° Fahr. Mixed with an equivalent weight of cupric sulphate, the two 

 salts separate if the solution be exposed to the air, but in closed tubes the 

 solution at 0° Fahr. forms beautiful feathery crystals, which melt rapidly 

 at 32°, without any separation of salt. 



Similar phenomena are produced by a supersaturated solution of zinc 

 sulphate and potash alum in equivalent proportions exposed to a tempe- 

 rature of 4° Fahr. A similar solution of the cupric and magnesic sul- 

 phates at — 4° also became solid, and melted rapidly at 32°. 



Experiments were also made with the sodic and magnesic sulphates, 

 cadmic, and some other sulphates. The addition of potassic sulphate to 

 other sulphates, in atomic proportions, forms double salts, which, so far 

 as they were examined, do not form supersaturated solutions. 



The effect of low temperatures was in some cases to throw down a 

 portion of the salts in the anhydrous form, upon which were formed by 

 repose crystals of a lower degree of hydration than the normal salt. Some 

 cases of this kind are described in the paper. 



VIII. "On Furfuraniline and Furfurtoluidine/'' By John Sten- 

 house, LLJD., F.R.S. Received May 19, 1870. 



In an epistolary communication to Mr. H. Watts * I stated that " The 

 most abundant and economical source of furfurol is in the preparation of 

 garancin by boiling madder with sulphuric acid. If the wooden boilers, 

 in which garancin is usually manufactured were fitted with condensers, fur- 

 furol might be obtained in any quantity without expense. Furfurol is 



* Watts's Dictionary, ii. 751. 



