Mr Hcrschel on the Hyposidiihurous Acid. 25 
Ignition and combustion may be maintained for any length of 
time, by cautiously adding small quantities of the substance* 
To analyse this salt, I counterbalanced a platina crucible, and 
introduced into it 100 grains concentrated sulphuric acid, which 
was warmed over a spirit lamp ; 100 grains of the hyposulphite 
were tlien added, which were decomposed with so little commo- 
tion, that I could scarcely believe, on weighing it, that nearly 25 
cubic inches of gas had made their escape, which was sulphurous 
acid. Being then fully ignited, 95.50 grains remained in the 
crucible. To ensure the complete conversion of the salt into 
sulphate, this was moistened vnth nitric acid, and again ignited ; 
95.50 grains were still found remaining. Hence 100 grains 
hyposulphite of lead are equivalent to 95.5 sulphate, and conse- 
quently contain 70.30 htharge. I had previously assured my- 
self, by ignition in glass vessels, that the salt under examination 
contained no sensible quantity of water, only a slight dew being 
evolved, hardly amounting to 0.1 in 100 grains. 
Hence we have for the composition of the salt. 
Oxide of lead, 70.30 
Acid, - 29.70 
100,00 
Now, if we compute the composition from the formula (/ -f O) 
4- 2. (S + O) where I 129-5 the number representing lead, 
we find 
Oxide of lead, 69.92 
Acid, - 30.08 
100.00 
The slight deviation in excess of about 4 parts in 1000 may be 
accounted for by a minute quantity of sulphate of lead in the 
acid used, though purified by distillation. 
When hyposulphite of lead is subjected to heat in a retort, 
over a lamp, it is converted into a black brilliant powder,, and 
loses 20 per cent, of its weight. The only product is sulphurous 
acid gas, which, received over mercury, is found to be perfectly 
pure, the air of the retort being allowed for. When fully 
ignited in a close crucible, it loses 20.60, but a small portion of 
this is sulphur, as in the experiment in close vessels, a minute 
