the Combinations of Phosphorus. 443 
will bear; and it is difficult to ascertain the precise weight of this, 
as the tube always unites with some phosphoric acid where it is 
red hot at its mouth ; but this can be only a trifling source of 
error. 
In these experiments, and in all the others detailed in this 
paper, 1 received much useful assistance from Mr. Faraday of the 
Royal Institution ; and much of their value, if they shall be found 
to possess any, will be owing to his accuracy and steadiness of 
manipulation. 
Experiment 1.—Six grains of phosphorus. The small tube 
with the phosphorus weighed before the combustion 56°5 grains ; 
after the combustion 50:9 ; so that it had increased 4-10ths; and 
this increase was in great measure from phosphorus that had 
escaped combustion ; and when this was burnt out by a strong 
red heat, the increase of weight of the tube was under 1-10th: 
so that at least 5‘9 of phosphorus had been converted into acid: 
23°5 cubical inches of oxygen were absorbed: thermometer being 
at 46° Fahrenheit; barometer 29-6 inches. 
Experiment 11.—Ten grains of phosphorus. The glass tube 
containing the phosphorus weighed 103°1 grains; after the ex- 
periment 95°6 ; but much phosphorus remained unconsumed. 
After the tube had been heated to redness, it weighed 94 grains; 
so that at least 8-4 grains of phosphorus were consumed in the 
first process. ‘The absorption of gas was 34 cubical inches. 
Barometer 29°8; thermometer 47°. 
Experiment I11.—Ten grains of phosphorus. By weighing 
the tube after the experiment, and then distilling and burning 
the residual phosphorus, it was found that 9-1 grains of phos- 
phorus had been burnt, which had absorbed 35°25 cubical inches 
of oxygen. Barometer 29-7; thermometer 49° Fahrenheit. 
I give these experiments as the most accurate I have made. 
The pressure aud temperature vary so little, that the corrections 
for them are of no importance. Supposing that 100 cubical 
inches of oxygen (the barometer being between 29°8 and 29°6, 
and the thermometer between 46° and 49° Fahrenheit) weigh 
33:9 grains, phosphoric acid will be composed, according to the 
first result, of 100 phosphorus to 135 oxygen; according to the 
second, of 100 to 137-2; and according to the third, of 100 to 
131-3: the mean will be 100 to 134°5. 
The light of the phosphorus burning in vapour in these expe- 
riments was excessively bright ; yet the top of the retort never 
became softened; and the phosphoric acid, which increased the 
weight of the tube, principally combined with the glass at the 
aperture where it was red hot. I cannot but consider this pro- 
cess of burning phosphorus in the gaseous state in a great ex- 
cess of oxygen, as the most accurate mode that has yet been ~ 
vise 
