Mechanical Sciencf^. 227 



ivory thus engraved is considerable. Mr. Cathery has much im- 

 proved and simplified the process, by coverini^ the ivory with 

 engraver's varnish, and drawing" the design with an etching 

 needle; he then pours on a menstruum, composed of 120 grains 

 of fine silver, dissolved in an ounce measure of nitric acid, and 

 diluted with one quart of pure distilled water. After half an 

 hour, more or less, ticcording to the required depth of tint, the 

 liquor is to be poured off, and the surface is to be washed with 

 distilled water, and dried with blotting paper. It is then to be 

 exposed to the light for an hour, after which the varnish may be 

 removed by means of oil of turj^entine. The design will now 

 appear permanently impressed on the ivory, and of a black or 

 blackish-brown colour, which will come to its full tint after ex- 

 posure for a day or two to the light. Varieties of colour may be 

 given by substituting the salt of gold, platina, copper, &c. for the 

 solution of silver. — Trans. Soc, Arts, xliv. 57. 



11. Method of Cuiiing Glass. — If a tube, a goblet, ot other round 

 glass body is to be cut, a line is to be marked with a gun-flint 

 Iiaving a sharp angle, an agate, a diamond, or a file, exactly on the 

 place where it is to be cut. A long thread, covered with sulphur, 

 is then to be passed two or three times round the circular line, 

 is to be inflamed, and burnt ; when the glass is well heated, 

 some drops of cold water are to be thrown on to it, when the pieces 

 will separate in an exact manner, as if cut with scissors. It is by 

 this means that glasses are cut circularly into thin bands, which 

 may either be separated from, or repose upon, each other, at 

 pleasure, in the manner of a spring. — Jour, de Connaissances 

 usuelleSy iv. p. 15, 



12. Preservation of Skins. — I. Stegar, a tanner, at Tyman, in 

 Hungary, uses with great advantage the pyroligneous acid, in pre- 

 serving skins from putrefaction, and in recovering them when 

 attacked. They are deprived of none of their useful qualities, if 

 covered by means of a brush with the acid, which they absorb very 

 readily. 



13. Indian Method of Varnishing. — The uncivilised Indians, 

 called Andoquies, who live near the sources of the river Magda- 

 lena, in Columbia, South America, use a vegetable substance as a 

 varnish, a specimen of which has been sent to the Society of Arts. 

 When taken from the shrub on which it grows, it is kept in water 

 to preserve it moist : when perfectly dry it is considered useless, as 

 those who work it up have no means of reducing it again to a 

 soft state. When about to be used, it is put into boiling water, to 

 separate from it the oily matter it contains. When eftectually 

 freed from the oil, it is taken out, and the varnisher puts a small 

 quantity into his mouth, and continues to chew it as he goes on 

 with his work. After thus chewing a bit of the varnish for some 



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