ImperfeB Conduclltig'pofvey of Charcoal. — New Air-pump. ^oT 



the fame fire, does not receive more than about two-thirds of the heat of a body furrounded 

 with quart7ofe fand ; that the reduction of metals which do not flow at a lower degree of 

 heat than 130 degrees, cannot be effefted in charcoal ; that the pyrometric pieces do not af- 

 ford an accurate judgment of the heat communicated, unlefs they be in contaft with fub- 

 ftances of the fame kind as thofe which furround the body, on which the chemical procefs is 

 performed ; and laftly, that with thefe attentions we may make an advantageous afe of this 

 inftrument, of which the applications will not be fufficiently known, until we fhall be able 

 to procure, at pleafure, cylinders fabricated after the manner of Wedgewood, of a clay fuf- 

 ceptible of lofing 0,18 of its volume by contraction ; or, which is the fame thing (fuppofing 

 po elaftic matter to fly off), of paffing from the fpecific gravity of 2,05 to 2,45, between the 

 degree of ignition required for baking the bifcuit of earthen ware, and the higheft heat ef 

 furnaces, without undergoing a commencement of fufion. 



I have made a great number of experiments, with the intention of difcovering a clay 

 which might naturally exhibit thefe properties, or which might acquire them by eafy and 

 cheap preparation. I hope I {hall be fhortly able to communicate fatlsfadlory refults to the 

 clafs of the inftitute. 



IX. 



]Defcripthn of an Air-pump, of a neiv ConflruB'ton. By the Rev. JaMES LiTTLE, of Lachtty 



m the County of Mayo, in Ireland*. 



HE pump here defcrlbed is a portable one, contrived fo as to be confined in a very 

 fmall fpace ; but the author obferves, that it may be made of a different form, and with two 

 barrels, though not conveniently. 



Fig. I. plate XXI. Is a perfpeftive view of the whole machine, as it lies before the 

 operator. Fig. 2. is a back view of the fame. 



- The barrel A A (fig. i.) is almoft fifteen inches long, and internally in diameter juft two 

 inches. The plfton (fig. 3.) is folid, without any perforation ; it confifts of circular plates 

 of leather, prefled together between the round plate a (in the focket of which, b, the pifton 

 rod was Inferted, and faftened by a crofs-fcrew, before the leathers were put on), and the two 

 upper plates c and d ; of which the outer one, d, being fcrewed upon a fcrew formed on the 

 outfide of the focket, prefl'es down the under plate, and this the leathers, which latter are 

 not reprefented in the figure. The upper plate, when fcrewed on, lies even with the upper 

 part of the focket, that when the piflon is raifed to the top, it may touch the plate covering 

 the upper part of the barrel, leaving no air above the pifton. Thefe two plates of the pifton, 

 cfpecially the lower one, are made fo large as juft to move in the barrel without touching 

 it, and care was takeft that when the pifton is put down, it fhould be every where in contacl 



'* Iriili Tranfaflions. VI. 319. The paper from which the above is abftra£led, could not be civen on 

 account of its extent. It occupies 77 pages. Some of the early air-pumps were made with an horizontal 

 fcarrel. There is a plate of one in Senguerdii Phiiofophia Naturalis, the ftcond edition of vvhicli, in 410, was 

 publiflied at Leyden, 1685. 



VoL.II.— Feb. i79p. 5? , with 



