Miscellanies. 409 
ance of the lamellar hydrate of magnesia of Hoboken, N. J.; and 
that of the aluminium has a bright sulphur yellow color, the crystals 
standing out from the sides towards the centre of the tube in which 
it was formed. Lt. Mather obtained about one ounce of each of 
these chlorides at a single operation for each.— Extract of a — 
of April 20, 1831, to thes Editor. 
6. Pure cheomite of potash —M. Zuber Bes published w process 
for examining this salt, by means of tartaric acid, which is considered 
as objectionable, on account of his selection of an acid, which is 
rarely found in a pure state, and which forms with a solution of the 
chromate, a very compound solution, in which the indications of re- 
agents are not precise. 
It is better to use colorless nitric acid, adding sliows half a part to 
the salt in solution, a drop of a solution of nitrate of baryta, will oc- — 
casion precipitation, if sulphuric acid is present, or, a like quantity of 
nitrate of silver, will cause the deposition of chloride of silver, should — 
 Mhuriatic acid contaminate it. Both chromates of baryta and silver, 
are soluble, to a considerable extent, in chromic and nitric acids, and 
if the reagents are not added. in excess, there is no precipitation, if 
pure chromate of " potash i is in solution. ‘An extension of this method 
furnishes us with the salt ina state of purity. The chromate of 
commerce is to be-re-crystallized to remove the silicate of alumina 
-and oxide of iron, dissolved in water, nitric acid to displace one half — 
of the chromic is added and the liquor heated; moist chromate of ba- 
ryta may be dropped in, until the heavy sulphate ceases to fall, the li- 
quor filtered, and chromate of silvermixed with it, so long as the curdy 
chloride is formed, when it is again filtered and the clear liquor evapo- 
_ rated to a salt and heated to redness in a platina dish; the mass dis- 
solved in water, affords crystals of the pure salt by slow evaporation. 
It is impossible to remove sulphate of potash from this salt by the 
processes of eeanyemlieaion and solution —A. A. Haves. i 
ja. 
7. Covering for wires.—Mr. A. A. n Pate: recommends mastic 
colored by vermillion, or otherwise, as a very excellent substance for 
covering the wires of galvanoscopes. Mr. H. melts it in a saucer 
and slides the wire under the surface of the resin, by fastening a stick 
across the saucer so as to have its edge dip; then it is wound ‘in a 
coil or spiral. . Its superiority is due to ae ‘tenacity when gently 
warmed. os 
