524

Buching Tube — Valve-Siphon.

[Book V.

No. 250 is from the “ Dictionnaire CEconomique,” Paris , 1732, 3d edit.Tome i, S64. It is obviously copied, with the distilling apparatus of whichit forms a part, from som'e older work. No. 248 differs in nothing fromthose belonging one of the Pharaohs , (No. 236,) while the forms of Nos.249 and 250 are evidently owing to the material of which they are made,viz. tinned iron; the legs were separate pieces, and their junction formedan acute angle.

The sucking tube is not figured by Decaus, Fludd, Moxon, Boyle, Beli-dor ; nor yet by Rohault, Gravesande, Desaguliers , and the Abbe Nollet ,although it was in use before the populär works of the last named authorswere published. Switzer, in his Hydrostatics, 1729, has figured a siphonfor transferring water over a hill with a short sucking tube attached ; butthis is placed near the top, and was designed to draw off the air thatmight accumulate at the bend after the instrument had been some timein use.

In Martin’s “ Philosophical Grammar,” Lond. 1762, sixth edit. No. 251is represented. The sucking tube appears but as the nucleus of themodern one, being a very short conical piece attached to the extremityof the discharging leg. The figure we suppose was in the previous edi-tions of the work. It was copied into the London Magazine for 1764,p. 584, and is there named " the syphon or crane in common use'' Butthe sucking tube was fully developed before these dates. In “ Arts etMetieres,” it is not curtailed of its fair proportions. The treatise on the Artof the Cooper, (Art du Tonnelier,) was published in 1763, and in it No.252 is given as the siphon then used in Paris for emptying wine casks, &c.It was made of tin plate, and for the convenience of hanging it up whennot in use, a ring was attached to the upper part. “ Ce siphon est connusous le nom de pompe." (Folio edit. p. 47.)

“ L’Art du Distillateur Liquoriste,” was published in 1775. In itanother valuable modification of the siphon is exhibited. See' No. 253.This in its outline resembles the preceding one, being made of the samematerial. It has no sucking tube, but the discharging leg is closed by acock, and the receiving one by a light valve opening inwards ; hencewhen once charged, this siphon would always remain so while the cockwas kept shut: it could be moved from one vessel to empty another atpleasure, for as soon as the end of the short leg was immersed and thecock opened, it would commence to act. This instrument was named“ siphon ä clapet (Folio edit. p. 140.)

The more common form of the siphon as now used is shown at No. 254,a valve in the short leg being dispensed with. Sm,all instruments areso easily charged, that little or no advantage is derived from keeping themfilled. Liquids confined in them become insipid, and in some cases taintedby the material of the tube ; besides, as small siphons are required todecant different liquids, their Contents must be discharged every time theliquid is changed. On these accounts the valve has been dropped. Thejunction of the sucking tube with the discharging leg must always be keptbelow the surface of the fluid to be drawn, as the virtual length of the legthere terminates. By means of the cock the dischrarge can always beregulated, and when a receiving vessel is filled—entirely stopped untilanother vessel is prepared.

Siphons with small syringes attached for the purpose of charging them,are frequently made by silversmiths for decanting wine from ordinarybottles, &c. See No. 255. The capacity of the syringe should equalthat of the siphon, as one stroke only (an upwai'd one) of the piston canbe used. Atnjospheric and forcing pumps are often used to charge very