G A Z

G A Z

( 531 )

taken to keep the retort itfelf as ftill as poffible,that none of its contents mix with thofe of thedecanter.

Another apparatus, fimilar to Dr. Nooth’s,but fomewhat better, is formed by the veffels a ,b and d of Fig. 42, adding to the top of d theveflel a of Fig. 44 . A valve is placed betweenb and d fimilar to that of Nooth’s apparatus.But as thefe veffels alfo belong to an improvedWoulfc’s apparatus, we {hall mention themunder that article.

It fhould be obferved however that the ut-moft effe£t of the belt glafs veffels in impreg-nating water with carbonic acid, or any othergas, is very far Ihort of the power of the forcingpump ; and it is by this latter method that allthe brilk foaming carbonated waters are made■which are confumed fo largely under the namesof artificial Seltzer, Soda, Pyrmont waters, &c.Mr. Paul, of Geneva, appears to have been thefir ft who adopted this excellent method ofmaking the artificial mineral waters.

G AZOMETER.

Thefe are veffels of various fhapes and con-trivance, intended as refervoirs to hold a prettylarge quantity of gas (feveral gallons for ex-ample) and are indifpenfible in a well-furniftiedlaboratory. They are made of thin tinnediron-plate, well japanned on both fides, andmoft of them have fome contrivance for mea-furing the quantity of gas which they contain.We {hall defcribe three kinds of gazometer, allof which aie in common ufe and anfwer verywell.

V. Fig. 61 and 62 reprefent a view andfeftion of a common gazometer. The lettersin each refer to the fame parts, a a is the outerpail or circular vefl'el, with a fpout at top. Twotubes d and e (each fitted with a ftop-cock ex-ternally) are firmly foldered to the fides of thepail: the tube d penetrates at the bottom ofthe pail and proceeds to the center where itjbins the- termination of the tube c, which entersthe top of the pail and proceeds downwards;and from the place of jumftion the upright tubeg rifes through the middle of the pail a littleabove the level of its upper rim. The vefl'el b isa cylinder open only at the bottom, and of lefsdiameter than the pail, into which it is in-verted, and can move up and down freely.This cylinder has a l'olid ftern c, which paffesthrough a hole in the wooden crofs bar of theframe round the top of the pail, and fervesboth to keep the cylinder in a perpendiculardirection when moving up and down, and to in-dicate the quantity of inciofed gas by the gradu-

ation on its furface. The weight of the cylin-der is counterpoil'ed by weights put in a Icaledifh, which is connected to the top of the cy-linder by a cord and pulley. The pail hasbefides an opening through its bottom ciofed bya feparate ftop-cock_/j by which the water maybe drawn off. The whole apparatus is conve-niently fupported on a heavy wooden ftool. Itis not efiential to have both the tubes e and d forthe filling and emptying of the gazometer, butit is more convenient, as they are of differentheights. To ufe this gazometer, firft let thecylinder fall to the bottom of the pail, and pourwater into the fpout of the latter till it is quitefull. Then fhut the cock e and open d andconned with it the tube which conveys the gasimmediately from the retort or other vefl'el inwhich it is produced; or, if more convenient,fhut d and convey the gas through e. In eithercafe the gas rifes through the upright tube « tothe top of the cylinder b , which it graduallylifts up, and care mull be taken to keep in thefcale difh fufficient weight to allow the cylin-der to move with perfect freedom. When allthe gas is obtained, fhut the cock throughwhich it palled, and it remains in the invertedcylinder ready for ufe. To take out a portionof it, conned with either of the ftop-cocks abent-tube dipping under the jar, or whateverveflel it is to be received in inverted over water,and at the fame time lift up the fcale difh, onwhich the cylinder will prefs down by its ownweight, and force out the contained air. Thetube which terminates at e is a very convenientheight for a blow-pipe, either for commonair or efpecially for oxygen gas, and ftraightblow-pipe tubes are made for the purpofe,which may be of the fize to fit on clolely,or may eafily be made to do fo, by the in-tervention of a cork. It fhould be obfervedthat in this apparatus the weight of the cylin-der is conftantly increafing in proportion as itfills with gas, and rifes out of the water, andconfequently if the counterpoifing weight isonly equal to that of the cylinder in the firftmoment of its rife, the gas becomes graduallymore and more compreffed by that part of theweight of the cylinder which is not counter-poifed, and if its quantity is then eftimated bythe bulk which it occupies, without makingallowance for the increafing preffure, a materialerror would arife. To compenfate for thisincreafin? weight of the cylinder, and render afcale of equal graduations t accurate, fome haveingenioully adopted the plan of a fpiral pulleyto the cord, which has the effe£! of gradually3x2