1872.] 



On Supersaturated Solutions of Glauber's Salt. 



109 



sent in urine is, however, so small that the precise nature of this substance 

 has not as yet been determined. 



Finally, the author points out an apparent connexion between this sub- 

 stance and alcohol. It was found that, after the elimination due to the 

 ingestion of alcohol had ceased, the amount of this substance eliminated in 

 a given time at first remained below the quantity normally excreted, and 

 only gradually rose again to the normal standard. A careful study of 

 this connexion may perhaps serve to throw some light upon the physiolo- 

 gical action of alcohol. 



III. "On the Action of Low Temperatures on Supersaturated Solu- 

 tions of Glauber's Salt." By Charles Tomlinson, F.R.S. 

 Received December 4, 1871. 



When a solution of the ordinary ten-atom hydrate of sodic sulphate, 

 saturated at about 93° F., its maximum point of solubility, is boiled and 

 filtered into a clean flask, which, being closed, is left to cool to 40° and 

 under, a modified or seven-atom hydrate is formed at the bottom of the 

 solution ; this increases in quantity as the temperature falls, and passes 

 into solution as the temperature rises ; and, so far, the observation is 

 supposed to be complete. 



But if a supersaturated solution of Glauber's salt be reduced from ordinary 

 atmospheric temperatures to low ones by means of a freezing-mixture of snow 

 and salt, the results obtained are so remarkable that I venture to think a 

 short statement of them may be worthy of a place in the 'Proceedings,' 

 by way of addenda to Section II. of my second paper " On Supersaturated 

 Saline Solutions," contained in the Philosophical Transactions for 18/1, 

 page 59. 



A solution of one part Glauber's salt in one of water was boiled and 

 filtered into a two-ounce flask that had been previously filled with strong 

 nitric acid and well rinsed with clean water. The solution was agaiu 

 boiled in this flask, into which a thermometer was passed, the stem being 

 surrounded by several turns of lamp-cotton, which served to close the 

 flask as soon as it was removed from the source of heat. 



Next day the flask was put into a freezing-mixture at about 15° F. 

 The solution slowly sank to 19°, when there was an abundant deposit of 

 crystals of a peculiar opaque white, not like the transparent octahedra 

 that are thrown down when these solutions cool to 40° and under, but 

 very much like the octahedral crystals formed during the cooling of a 

 strong solution of sal-ammoniac. There were tufts of regular octahedra 

 and fern-like crystalline forms. During their formation the thermometer 

 rose to 26°. The flask was now transferred to water at 48°, when the 

 opaque-white crystals broke up into an amorphous woolly mass. As the 

 temperature of the solution rose to 40°, then for the first time the usual 

 transparent octahedra of the anhydrous salt fell down. Next day the 



