130 Dr Davy's MisceUaneotis Chemical Observations. 



be allowed to subside in the dark, and the subsidence should be 

 complete before the fluid is decanted and exposed to light. 



4. On the Solubility of Phosphorus in Water. 



Phosphorus is commonly considered insoluble in water. From 

 some observations which I have made, I infer that it is very 

 slightly soluble. 



Distilled water (a phialful, well corked and inverted), in 

 which a piece of phosphorus had been immersed twenty-four 

 hours, filtered, had a distinct odour of phosphorus, and was 

 just perceptibly luminous in the dark. 



The experiment repeated, using water impregnated with 

 carbonic acid gas, with sulphurous acid gas, and with nitrous 

 gas, indicated the same. In each instance, the water, after ha- 

 ving been filtered, smelt of phosphorus, but was not distinctly 

 luminous. 



If there is no fallacy in the results, (and I am not aware of 

 any), they seem to warrant the above conclusion. 



5. On the Temperature at which Phosphorus melts. 



According to Pelletier, phosphorus melts at 99° ; according 

 to Dr Thomson, at 108°. * 



The phosphorus which I have tried, melted at 112°. At 

 110°, I have found it brittle, and very easily reducible to pow- 

 der. Gradually, and very slowly cooled, in a solution of pot- 

 ash, I have seen melted phosphorus liquid at 72° ; then, when 

 touched with the thermometer, it suddenly became solid. 



6. Solution of Potash as a Eudiometrical Test. 



I believe that a strong solution of potash may be usefully 

 employed in eudiometrical researches with phosphorus, to as- 

 certain quickly, and with certainty, without calculation, the 

 exact quantity of azote. This opinion is founded on the fact, 

 that potash separates phosphorus from azote ; and the results 

 of the eudiometrical experiments in which I have tried it, are 

 favourable to its correctness. 



• System of Chemistry, 5th edition, i. 261. 



