+ 
392 Hydrogen gas apparatus. 
M. Wadell, who has seen this process practised in Chi- 
na, has applied it successfully to the preparation of zinc 
plates for galvanic apparatus. 
: Bul. de la Soc. d’encour. 
- 98. Willis? Jute.—To prevent the materials contained in 
earthen crucibles and retorts from penetrating through 
their substance, the author prepares a lute composed 
of two ounces of Borax dissclved in a pint of boiling wa- 
ter, to which is added slacked lime in sufficient quantity to 
form a soft paste. This lute applied to the vessel by a 
brush within and without (if a crucible) vitrifies_ very 
speedily, and prevents the penetration of the melted in- 
gredients, but it cannot prevent the fracture of the vessel. 
To accomplish this second object, the inventor covers re- 
torts with a lute composed of linseed oil and slacked lime. 
This is applied by a brush to retorts, and left to dry during 
a day or two. It can be taken every time a retort is char- 
ed to cover it with this lute, it may be used four or five. 
times without breaking. Cracks may be effectually stop- 
ped by the same composition, only powdering the surface 
with a little slacked lime. This may be done without risk 
even when the retort is very hot. 
39. Hydrogen gas apparatus.—An instrument much 
used in Germany and Russia, resembles the bottle of Gay 
Lussac, except that the zinc is not suspended from the top, 
but supported from the bottom on a tripod of lead, which 
is not attacked by the sulpburic acid. When the stoppet 
is opened, the gas escapes, the acid ascends and covers 
e zinc and the action is renewed; but as soon as the 
acid touches the zinc, the lead which before produced no 
change, furnishes on all sides a great quantity of little bub- 
bles of gas, and more copiously than the zinc itself. This 
resulis evidently from the galvanic action arising from the 
contact of the zinc and lead; but what is the most surpri- 
sing is the prodigious. effect of this pile of a single element, 
compared with the weak effect of ordinary piles. 
~ Journal des mines. 
30. Method of discovering very small quantities of mer 
cury.—All the oxides and saline compounds of mercury, 
placed upon gold in a drop of muriatic acid with a piece 
