4c8 Sir H. Davy on some Combinations 
at tlie surface of the liquid. This substance may be called 
hydrophosphorous acid ; for it consists of pure phosphorous 
acid and water. This is proved by the action of ammoniacal 
gas upon it ; when it is heated in contact with ammonia, water 
is expelled and phosphite of ammonia formed; and it is like- 
wise shewn by the results of its decomposition in close vessels, 
which are phosphoric acid and a peculiar compound of phos- 
phorus and hydrogen. 
Ten parts in weight of the crystalline acid I found produced 
about 8.5 parts of solid phosphoric acid, and the elastic pro- 
duct must of course have formed the remainder of the weight, 
allowing for a small quantity of the substance not decom- 
posed. 
The peculiar gas is not spontaneously inflammable; but 
explodes when mixed with air, and heated to a temperature 
rather below 212 0 . 
Its specific gravity appeared from an experiment in which 
a small quantity of it only was weighed, to be to that of air 
nearly as 87 to 100. Water absorbed about one-eighth of its 
volume of this gas. Its smell was disagreeable, but not nearly 
so fetid as that of common phosphuretted hydrogene. 
When it was detonated with oxygene, it w ? as found that 
three of it in volume absorbed more than five in volume of 
oxygene, and a little phosphorus was precipitated. 
When potassium was heated in contact with it, its volume 
increased rapidly till it became double, and then no further 
effect was produced. The potassium was partly converted 
into a substance having all the characters of phosphuret of 
potassium ; and the residual gas absorbed the same quantity 
of oxygene by detonation as pure hydrogene. When sulphur 
