VOL. IX.] PHILOSOPHICAL TRANSACTIONS. J 83- 



ciit through the middle, it will in a moment change from a pale yellow to a deep 

 purple or blue, and stain linen accordingly. A drop of the juice, leisurely 

 squeezed out, holding it between your eye and the light, will change through 

 all the colours of the rainbow, in the very time of its falling, and fix in a purple, 

 as it does in the springing out of its veins. 



VII. Of the speedy vitrifying of the whole Body of Antimony hy Cauh. 



The several vitrifications of antimony are either opake or transparent. To 

 the first kind I shall add one, which is in itself very curious, and has these 

 advantages above the rest, that it is done with great ease and speed; and by 

 it I have performed some things on minerals and metals, which with crude 

 antimony alone I could not effect. Take of antimony one pound ; flux it 

 clear : have an ounce or two of the cauk-stone, described below, in a lump 

 red-hot in readiness. Put it into the crucible to the antimony ; continue the 

 flux a few minutes: cast it into a clean and not greased mortar, decanting the 

 melted liquor from the cauk. This process gives us above ]5 ounces of 

 vitrum of antimony, like polished steel, and as bright as the most refined 

 quicksilver. The cauk seems not to be diminished in its weight, but rather 

 increased ; nor will be brought to incorporate with the antimony, though 

 fluxed in a strong blast. 



This cauk-stone is a very odd mineral, and I always looked upon it to be 

 much akin to the white milky mineral juices, I formerly sent you a specimen 

 of: and this experiment is demonstrative that I was not mistaken; for the 

 milky juice of the lead mines vitrifies the whole body of antimony in like 

 manner. That this vitrification is from the proper nature of cauk I little 

 doubt ; for I could never light upon any one mineral substance, which had 

 any such effect upon antimony; and I have tried very many, as lapis calaminaris, 

 stone sulphur, or sulphur vivum, galactites, sulphur marcasite, alum-glebe, 

 divers spars, &c. Cauk is a ponderous white stone, found in the lead-mines; 

 it will draw a white line like chalk or the galactites: and though it be so free, 

 it is more firm, and has a smooth and shining grain, spar-like, yet not at all 

 transparent. — [Cauk, or cawk, is a sulphate of barytes.] 



An Account of some Books. N° 110, p. 226. 



I. Tracts containing — 1. Suspicions about some Hidden Qualities of the Air, 

 with an Appendix touching Celestial Magnets, and some other Particulars. — 

 2. Animadversions upon Mr. Hobbes's Problemata de Vacuo. — 3. A Discourse of 

 the Cause of Attraction by Suction. By the Hon. Robert Boyle, Esq. F. R. S. 

 London, l674, in 8vo. 



