10 OPERATIONS AND INSTRUMENTS 



sometimes done. Glass retorts are generally 

 placed in a sand-bath, or suspended over a lamp, 

 for which Argand's lamp is the best. The re- 

 ceiver is placed upon some stand convenient for 

 the purpose, with a ring made of hay under it, or 

 some such contrivance, to keep it steady. 



A (Fig. 2.), is a vessel called a mattrass, for the 

 same purpose, having a vessel, B, called an alembic, 

 fitted to the head. The liquid raised by heat into 

 the state of vapour, is condensed in the alembic, 

 and falls into a groove all round its inside, from 

 whence it runs out by the spout, C, into the re- 

 ceiver, D. 



Fig. 3. are conical tubes that fit into another, 

 for lengthening the necks of retorts, &c. to con- 

 nect them with the receivers at any distance: they 

 are called adopters. 



Fig. 4. are phials with bent glass tubes fitted in 

 them, for disengaging gases, and similar experi- 

 ments : they were used by Priestley, and are 

 hence called Priestleij^s bottles, and sometimes 

 proofs : they are either tubulated or plain. 



A (Fig. 5.), represents a common still. It is a 

 large vessel of copper, into which the materials 

 to be distilled are put. The still is built up in 

 brick-work, which covers it up to the neck; the 

 fire is applied underneath, and runs round it in a 

 spiral manner. B is the Jiead of the still. This 

 head is connected with the ivorm, which is a spiral 

 tube, immersed in a vessel of cold water, called the 

 refrigeratory, or cooling tube, C. The liquor be- 

 ing condensed in its passage through the worm, 

 runs out at the cock, D, into the vessel placed 

 there to receive it. 



This is the construction of the common still for 

 distilling spirituous liquors ; but a very great im- 



