LABORATORY. 



and an empty bladder, or bottle of elas- 

 tic gum, furnished with a stop cock, is to 

 be screwed on a. When the vessel, c, is 

 pressed down by the hand, the gas passes 

 down the centnil pipe, which it had be- 

 fore ascended, and its escape at b being 

 prevented, it finds its way up a pipe 

 which is fixed on the outer surface of the 

 vessel, and which is terminated by the 

 cock, a. liy means of an ivory mouth-piece 

 screwed on this cock, the gas included in 

 the instrument may be respired ; the 

 nostrils being closed by the fingers. 

 When it is required to transfer the gas 

 into glass jars standing in water, a crook- 

 ed tube may be employed, one end of 

 which is screwed upon the cock, b, while 

 the other aperture is brought under the 

 inverted funnel, fixed into the shelf of the 

 pneumatic trough. 



Several alterations have been made in 

 the form of this apparatus, but they are 

 principally such as add merely to its neat- 

 ness and beauty, and not to its utility ; 

 and they render it less easy of explana- 

 tion. The counterpoises, e e, are now 

 generally concealed in the framing, and 

 the vessel c is frequently made of glass. 



When large quantities of gas are re- 

 quired (as at a public lecture) the gas 

 holder, fig. 9, will be found extremely 

 useful. It is made of tinned iron plate, 

 japanned both within and without. Two 

 short pipes, a and c, terminated by cocks, 

 proceed from its sides, and another, 6, 

 passes through the middle of the top or 

 cover, to which it is soldered, and reaches 

 within half an inch of the bottom. 



It will be found convenient also to have 

 an air cock with a very wide bore fixed to 

 the funnel at b. When gas is to be trans- 

 ferred into this vessel from the gazometer, 

 the vessel is first completely filled with 

 water through the funnel, the cock a be- 

 ing left open and c shut. By means of an 

 horizontal pipe, the aperture a is connect- 

 ed with a of the gazometer. The cock b 

 being shut, a and c are opened, and the 

 Vessel c of the gazometer, fig. 8, gently 

 pressed downwards with the hand. The 

 gas then descends from the gazometer 

 till the air-holder is full, which may be 

 known by the water ceasing to escape 

 through the cock c. All the cocks are 

 then to be shut, and the vessels disunited. 

 To apply this gas to any purpose, an 

 mpty bladder may be screwed on a; 

 and water being poured through the fun- 

 nel b, a corresponding quantity of gas is 

 forced into the bladder. By lengthening 

 the pipe, b, the pressure of a column of 

 Water may be added ; and the gas being 



forced through a t with considerable velo- 

 city, may be applied to the purpose of 

 a blow-pipe, &c. 8cc. 



The gazometer, already described, is 

 fitted only for the reception'of gases that are 

 confinable by water, because quicksilver 

 would act on the tinning and solder of 

 the vessel, and would not only be spoiled 

 itself, but would destroy the apparatus. 

 Yet an instrument of this kind, in which 

 mercury can be employed, is peculiarly 

 desirable, on account of the great weight 

 of that fluid ; and two varieties of the mer- 

 curial gazometer have therefore been in- 

 vented. The one of glass is the contri- 

 vance of Mr. Clayfield, and may be seen 

 represented in the plate prefixed to Mr. 

 Davy's researches. In the other, invent- 

 ed by Mr. Pepys, the cistern for the mer- 

 cury is of cast iron. The drawing and 

 representation of it may be found in the 

 fifth volume of the Philosophical Maga- 

 zine; but as neither of these instruments 

 are essential to the chemical student, and 

 as they are required only in experiments 

 of research, we refer to the minute de- 

 scriptions of their respective inventors. 



Very complete sketches of chemical 

 instruments and furnaces may be seen in 

 Henry's chemistry. 



After the general description we have 

 here given of the arrangement and appara- 

 tus for chemical experiments, we shall 

 conclude with a short account of the 

 blow-pipe. 



It is a tube which terminates in a per- 

 foration not exceeding the hole which 

 might be made by a small pin. There is no 

 difficulty, in case of emergency, in making 

 one out of a tube of glass, and the com- 

 mon blow-pipes sold at the ironmongers 

 for a few pence, and in universal use with 

 workmen, are very good. Others more 

 costly and elegant, which have a small 

 space for the condensation of the vapour 

 of the breath, are sold by the makers of 

 chemical apparatus. It requires some 

 address to produce a constant stream of 

 air by blowing through this pipe ; but the 

 principal artifice consists in keeping the 

 tongue to the roof of the mouth, and 

 using the breath by the pressure of the 

 muscles of the face instead of the chest. 

 Some workmen in glass contrive to hold 

 the pipe steady between the teeth, and by 

 that means have both hands at liberty tor 

 use ; but as this requires uncommon 

 steadiness in the head, the philosophical 

 chemist will probably prefer fixing his 

 pipe to one of his stands Some blow- 

 pipes have been made, through which a 

 a stream of vapour from boiling alcohol is 



