Composition of Enamel* 898 
rent colours. It might be attended with advantage to try 
some of these combinations. Ponderous earth (barytes) 
and lime fuse very well together : by adding a little silex, 
or a little magnesia, it is probable that an excellent mat- 
ter might be produced. If this glass, composed of lime 
and barytes only, had sufficient solidity to resist the ail* 
and weak acids, there would be no necessity perhaps to 
add silex ; but if the marine salt, as I am inclined to think,, 
ought also to enter into the composition of this kind of 
glass, silex ought likewise to form a part of it. The ex- 
periments on this head, for the sake of trial, may be va- 
ried different ways. When the glass destined to serve as 
flux for colours is employed, it is customary, in order that 
they may be rendered more fusible, to add a little nitre 
and borax. The common borax of the shops contains an 
excess of soda, which, in my opinion, it would be of 
benefit to saturate with the nitric acid. I think also that 
the flux might be rebaked with the dose of nitre and 
borax, or of nitric borax, which might be added be- 
fore being employed. It is only to colours such as 
purple and the oxyd of cobalt that nitre and borax are 
added. 
I have tried to find a substitute for marine salt in the 
composition of white enamel. Potash produced only an 
ugly and ill fused gray mass, which acquired no lustre 
in the furnace; nitre produced a green mass, but exceed- 
ingly friable; sulphat of potash produced very nearly the 
same effect, only the mass was a little whiter: but nei- 
ther of these enamels was worth any thing. I did not 
try pure soda : I have, however, heard common soda ex- 
tolled ; but as it contains a great deal of marine salt, it 
must undoubtedly be on account of this salt that it pro- 
duces a good effect. Pure soda may nevertheless be 
tried, either alone or with marine salt; it perhaps might 
produce no bad effect with potash. 
Tol. ii. S c 
