Famish for preserving Metals froni Aci'h. 13 



Note. No apprehension need be entertained respecting 

 the effect of steeping marked cloths in an'ulkaline ley ; it 

 js an operation which is speedily performed without any- 

 perceptible loss of potash or of soda, if you first proceed to 

 wash with ley, for which purpose that which is left may be 

 again employed. If, conformably to the practice. 1 have 

 followed for a number of years, the alkalies for leys were 

 made caustic with quicklime, a great quantity of soda and 

 potash would be saved, and at the sanie time a superior 

 effect would be produced. 



HI. A Famish which preserves Fcssels made of Copper or 

 other Metals from the Action of Acids of a certain 

 Strength. By M. Hauffman*. 



1 o obtain from copal a varnish fit for this purpose, of a 

 whiteness and transparency resenibling water, it is necessary 

 to employ copal reduced to a very fine powder, and to expose 

 it, with twelve parts of fine oil of turpentine, for some hours^ 

 or till It is completely dissolved, to the moderate heat of a 

 sand-bath, in a capsule of glass, stone, or porcelain ; ob^ 

 servmg to stir the whole very often with a glass rod. It is 

 at the moment when it begins to acquire the consistence 

 of syrup that the total dissolution of the copal takes place 

 by means of the stirring, which is facilitated by the occa- 

 sional addition of a small quantity of oil of turpentine to 

 replace that which evaporates. Three-fourths of the oil of 

 turpentine which are lost by the evaporation in open vessels 

 maybe saved by making ^he solution in a long-necked 

 matrass, exposed to a sand-bath a sufficient time^to com- 

 plete the dissolution of the copal, shaking it at the same 

 time very frequently. The varnish obtained by one or the 

 other of these methods turns of a yellowish colour if the 

 heat be too violent; and as its application would be difficult 

 when its ccmsistence too nuich resembles that of honey, it 

 is adyiseable, instead of diluting it with oil of turpentine, 

 to mix it with one- fourth or (me-iiflh of its weight of al- 

 cohol ; taking care not to put more than is necessary, for 

 ai) ex-cess would turn it to a milky white by the precipita 

 lion of part of the copal, which admits into solution with it 

 only a certain quantity of alcohol without being precipi- 

 tated. Vessels of copper, or of any other metal, may re- 

 ceive one, two, or three coats of this varnish, and ought 

 each time to be thoroughly dried in an oven; after winch 



• Fi-onj tlic .iitnalcs de Chhnie, No. i:;8. 



they 



