226 Miscellaneous Intelligence. 



The description thus given is with reference to moulding those 

 bodies which cannot be so done by any other than an elastic mould ; 

 but glue moulds will be found greatly to facilitate casting in many 

 departments, as a mould may be frequently taken by this method 

 in two or three pieces, which would, on any other principle, require 

 many. — Trans. Soc. Arts, xliv. 38. 



8. Leslie* s Apparatus for ascertaining the Specijic Gravity of 

 Powders*. — Relative to the instrument constructed lately by Mr. 

 Leslie, for the purpose of ascertaining the density of powders, the 

 Bulletin Universelle observes, that it is the same with the Stereo- 

 meter of M. H. Say, the description of which with figures may be 

 found in the 23rd volume of the Annales de Chimie, (1797,) at 

 page 1. The instrument was made and often used, especially in 

 ascertaining the specific gravity of gunpowder ; it still exists in the 

 collection of I'Ecole Polytechnique. — Bull. Univ. A. tome vi. p. 

 361. 



9. Menstruum for Biting-in on Plates of soft Steel. — This men- 

 struum, the result of the investigations of Mr. Humphrys, consists of 

 a quarter of an ounce of corrosive subHmate powdered, and a 

 quarter of an ounce of alum powdered, dissolved in half a pint of 

 hot water. It must be allowed to cool before being used, and when 

 on the plate, it is to be stirred continually with a camel's-hair 

 brushj and the plate washed perfectly after each biting. As the 

 acid, though clear at first, becomes turbid during its action on 

 the steel, it may be prudent, in fine works, to throw away each 

 portion of acid after it has been on the plate. The taste and ex- 

 perience of the artist must dictate the length of time he may leave 

 it on his plate ; delicate tints are obtained in about three minutes. 

 The process of biting is much more difficult of performance on 

 soft, than on hard, steel, perhaps in consequence of the proportion 

 of carbon in the latter, which affects the state of the iron when 

 taken into solution : for, by soft steel, engravers mean not a steel 

 that has been heated and cooled slowly, in contradistinction to one 

 that has been hardened, for they always work upon steel as soft as 

 it can be rendered, without change of composition ; but he under- 

 stands a steel that has been decarbonised, and brought back 

 towards the state of iron. The difficulties which have usually 

 occurred with such partially-decarbonised steel are removed, ac- 

 cording to the experience of the artists who have tried Mr. 

 Humphry's menstruum, by its substitution for the solvents pre- 

 viously resorted to. — Trans. Soc. Arts, xliv. 53. 



10. Etching on Ivory. — The usual mode of ornamenting ivory 

 in black is to engrave the pattern or design, and to fill up the 

 cavities thus produced with hard black varnish. The demand for 



* See Quarterly Journabxxi. 374. 



