lO 'Re.fearchcs rcJpeEi'ing the 



to it than thofe in which there are metallic calces. Thdfc, 

 therefore, which have been made with (ilex, chalk, and hor 

 rax, or white glafs, borax, and a little white ox^^d of anti- 

 mony, with a little nitre, as I have already mentioned, ought 

 to be employed with it. Purple will bear from four to twenty 

 parts of flux, and even more, according to the (liade required. 

 Painters in enamel employ generally for purple a flux which 

 they call brilliant white. This flux appears to be a femi- 

 opake enamel, vi^hich has been drawn into tubes, and after- 

 wards blown into a ball at an enamcller's lamp. Thefe bulbs 

 «ire afterwards broken in fuch a manner that the flux is found 

 in fijiall fcales, which appear like the fragments of fmall hol- 

 low fpheres. Enamel painters mix this flux with a little 

 nitre and borax. This matter, which produces a very good 

 effeft, I employed, without attempting to decompofe it. It 

 may be a very furil>le common white enamel which has been 

 blown into that form. It is to be remarked, that purple will 

 not bear a llrong heat. 



We have no metallic oxyd capable of giving dirc6lly a 

 fufed red; that is to fay, we have no metallic calces which, 

 entering into fufion, and combining under the form of tranf- 

 parent glafs v/ith fluxes or glafs, give direftly a red colour. 

 To obtain this colour it muft be compounded different ways, 

 as follows : — ^Take two parts, or two parts and a half (you 

 may,'however, take only one part,) of fulphat of iron and of 

 fulphat of aluminc ; fufethem together in their water of cryf- 

 tallifation, and take care to mix them well together. Con- 

 tinue to heat them to complete drynefs; theii incrcafe the 

 fire fo as to bring- the mixture to a red heat. The lall 

 operation nuifl be performed in a reverberating furnace. 

 Keep the mixture red until it has every where aflumed a 

 beautiful red colour, which you may afcertain by taking out 

 a little of it from time to time, and fuflering it to cool in the 

 air. You may then fee whether the matter is fuffieiently 

 j-ed : to judge of this it mufl be left to cool, becaufe while 

 hot it appears black. The red oxvds of iron give a red co- 

 !')ur; but this colour is exceedingly fugitive; for, as foon as 

 the oxyd of iron enters into fufion, the portion of oxygen 

 whi'^h gives it it^ red colour leaves it, and it becomes black, 



ycllowj 



