^6 Mr Herschel on th€ H^poitulphurous Acid, 
quantity of sulphur, varying from 0.2 to 1.0 per cent, sublimes 
into the neck of the retort. Regarding this residuum as a sul- 
phuret of lead (of which it certainly has all the appearance), I 
was kept for some time under the erroneous impression that 
2 S 4- O must be the formula of composition of the hyposul- 
phurous acid. Convinced, however, by the whole tenor of the 
preceding results, and their exact coincidence -with 2 S -f- 2 O, 
it becomes necessary to consider it as a sulphuretted oxide 
(Z 4- O + S) or 1 atom litharge 4- 1 atom sulphur, which agrees 
precisely with a loss of 20 per cent, sulphurous acid. 
Hyposulphite of Silver . — When a solution of pure crystal- 
hzed oxynitrate of silver, considerably diluted, is added cauti- 
ously, drop by drop, to a very dilute solution of any hyposul- 
phite, a white cloud is first produced, which redissolves on agi- 
tation. On adding more of the precipitant, the cloud reappears 
and aggregates into a dirty grey flaky precipitate, which sub- 
sides without any farther change of colour. The liquid has now 
acquired a very sweet taste*, and is not precipitated by muriate 
of soda, though hydrosulphuret of ammonia throws down sul- 
phuret of silver from it. On the addition of yet more of the 
precipitant, the grey precipitate changes rapidly to brown, and 
finally assumes the deep blackness and curdled appearance which 
characterize sulphuret of silver. The liquid has now entirely 
lost its sweet taste ; and, if tested with a muriatic solution, the 
presence of undecomposed nitrate is rendered sensible. This 
grey precipitate seems to be an hyposulphite of silver ; but it is 
manifestly extremely difficult, even in dilute solutions, and alto- 
gether impossible in concentrated ones, to hit the exact point 
without converting any portion into sulphuret. When the 
nitrate is added at once to a dilute hyposulphite, to decompose 
the whole of its acid, the precipitate is at first a white light 
cloud, which undergoes a rapid aggregation into flakes, changing 
its colour, as its consistency increases, from white to light yellow, 
* The sudden production of intense sweetness, on mixing two such disgustingly 
bitter liquids as nitrate of silver and hyposulphite of soda, is very striking, and 
shows how little we know of the way in which bodies affect the organs of taste. 
Sweetness and bitterness, like acidity, seem to depend on no particular principle, 
but to be regulated by the state of combination in which the same principles exist 
at different times. 
