aS Luminous Borax.— New Air Pump. 



petre in folution Is never heated to boiling, the fait does not remain In the boiler, and the- 

 evaporation is almofl: nothing. 



Vt. 



On the Light emitted by Super/aturated Borate of Soda, or Common Borax. By- Air, F. ACCUM, 



To Mr. Nicholson^ 

 SIR, 



JL HAT two flints and fevcral other filiceous flones, ftruck againft each other, appearJu— 

 minous on the fide ftruck upon ; and that phofphate of lime, tremollte, fugar, gum elemii . 

 black jack, and various refins-become luminous, and emit phofphoric fparJcs in the dark, 

 when fcratched with a (harp inftrument, or ftruck againft one another, are well known 

 to every tyro of natural philofophy ; but th'nt fuperfaturated borate offoda poffefies this pro*- 

 perty in the higheft degree, has not perhaps been hitherto remarked. Two pieces of this 

 fait, of confiderable magnitude, ftruck againft anotljer,. or a fwift blow with any fliarp in- 

 ftrument upon it, produces fuch a flafti of white light, as none of the before-mentioned 

 fubftances are capable of giving. It deferves therefore a place under the ciafs of thofe 

 kinds of phofphoric fubftances which give a perceptible light by attrition or percuflion, 

 without having been expofed either to the folar or artificial light ; for which reafon I take 

 the liberty of laying this before you, begging you will give thefe lines a place ia your- 

 much-admired Journal of Natural Philofophy . 



I remain. Sir, your very humble fervant, 



FREDERICK ACCyM. 

 Hay- Market, No. 17. 



VII. 



Neiu ConJlruElion of the Air Pump. By Sir G£ORGE S. Mackenzie, Bart. 



Jr IG. I. plate I, reprefents a fcdion of the barrel. C is a cup for oil to moiften the collar 

 of leathers L, in which the pifton rod R works. ?i is a plug— P P P P is the pifton, which is 

 folid, except a fpace for a collar of leathers ^, through which the wire W attached to the 

 valve V, pafles into a perforation in the pifton rod. N is a fmall nut to prevent the valve 

 from rifing too high. This method of lifting the valve was invented many years ago by 

 Dr. Rutherford of "Edinburgh. X is a perforation in the fide of the bottom of the barrel, 

 into which is inferted a piece of metal, as in fig. 5, with a filk valve tied over it, opening 

 downwards into the pipe K. E is the pipe leading to the receiver. 



The conftrudion of the bottom of the barrel is feen in fig. 2 and 3. Fig. 4 is the 

 valve and wire. Fig. 5 ftiews the conftrudlion of the pipe E leading to the receiver, which 

 is better than bent.copper.tubcs, as thefe are apt to crack. Fig. 6 is caft folid and bored. 



Figt 



