754 



DISTILLATION. 



ether, &c. are called retorts ; the vessel that receives 

 the distilled matter being called a receiver. See Chemi- 

 cal Apparatus, under Chemistry. 



The retort is the most simple of the distilling appa- 

 ratus, but it can only be employed when the vapour is 

 easily condensible, or when little heat is applied. When 

 expedition is an object, recourse is had to a more com- 

 pound apparatus, by which the condensation is facili- 

 tated. It is to this that the name still is more proper- 

 ly applied. 



The most simple of this variety is the alembic. It 

 consists of a lower vessel, terminating in a narrow neck, 

 which, with the substance that is to be distilled, is ap- 

 plied to the fire. At a certain height, depending on 

 the nature of the substance, is placed upon the neck, a 

 spacious vessel, which is exposed to the air, or kept 

 cold by a supply of cold water, in order to condense 

 the vapour as quick as possible. If exposed to the air, 

 it should be painted of japanned black. Round the bot- 

 tom of the interior is a projecting channel to receive 

 the liquid arising from the condensation of the vapour, 

 which runs down the sides of the open vessel, in pre- 

 ference to falling back into the still. From this chan- 

 nel, the liquid descends by a pipe, placed at a certain 

 angle into a receiver. This apparatus is sometimes 

 made of glass, for small experiments, but more fre- 

 quently of metal. It is at present not often used, the 

 condensation by the worm tub being much more ef- 

 fective. 



When the worm tub is employed, the still requires to 

 have such a shape, that the greatest possible surface may 

 be exposed to the fire. For this purpose, it is made in 

 the form of a frustum of a cone, the base being as 

 large as convenient, and the altitude very little. The 

 neck should be of such width, as to convey the vapour 

 as fast as formed. The height of the neck is regulated 

 by the nature of the substance. If it is mucilaginous, 

 such as the wash from which spirit is distilled, the 

 neck should be longer, to prevent its boiling over. 

 The exterior surface of the descending part of the neck, 

 in this case, should be polished, to prevent the escape 

 of heat. The descending part, at the same time, should 

 be painted black. The end of the latter is inserted in- 

 to the neck of the worm. 



The worm tub consists of a wooden vessel, about six 

 or eight times the capacity of the still. The length to 

 the diameter is about 10 to 7- The worm consists of 

 a spiral tube, which enters on one side of the tub, at 

 the top : it then passes spirally, in about six or eight 

 convolutions, to the bottom, where it comes out of the 

 side, in order to discharge the liquid arising from the 

 vapour condensed within it, by the agency of the cold 

 water, with which the tub is filled. The water is con- 

 stantly changing, by the warm water running away 

 from the top, whilst a supply of fresh cold water comes 

 in at the bottom. The section of the tube being a cir- 

 cle, its capacity should not be less than one-fifth of 

 that of the still : the diameter of the ends of the tube 

 being about three to one. The object is not merely to 

 effect a condensation, but to cool the liquid, so that it 

 may be less liable to evaporation after coming over. 

 The proportions of the means of condensation to that of 

 evaporation, will not always depend upon the relative 

 sizes of the vessels, but will be governed by the quan- 

 tity of vapour supplied in a given time, and the sup- 

 ply of cold water. In order to enter into the subject 

 theoretically, by which we shall be enabled to give a 

 more enlightened view of this branch of art, we shall 

 divide it into two heads, namely, Evaporation and Con- 

 1 



densation. The first will comprise the quantity of heat 

 taken by different liquids to become vapour, and the 

 means of furnishing the heat at the expence of fuel, 

 with the best means of applying and regulating the 

 latter. The second head will embrace the transference 

 of the caloric from the vapour to some other medium, 

 such as cold water, and the means of furnishing an ade- 

 quate supply. To the above it may be necessary to 

 add the different means of rendering substances less vo- 

 latile which are not intended to rise, and of giving great- 

 er volatility to those which are wished to be procured. 

 In the application of fire to a vessel containing a sub- 

 stance to be evaporated, the fire should be so placed 

 upon a grate, that a due supply of air may be admitted 

 to produce a vigorous combustion. No air should be 

 supplied but through the grate ; and the quantity of 

 heat will be the greatest, when no more air enters than 

 is sufficient for the combustion, an escess serving only 

 to cool what the fire has heated. The escape of the 

 smoke and hot vapour should be at a point not higher 

 than the level of the grate. This is to prevent the 

 heated matter from escaping before it has parted with 

 its heat to the vessel, by which its specific gravity is 

 increased, and it descends in consequence. When the 

 bottom of the vessel to be heated is circular, which is 

 the case with the common spirit still, the exterior sur- 

 face being also concave, the fire should be placed in 

 the middle of the circle. The flame and heated va- 

 pour first rises up against the middle of the concave 

 bottom ; it then should take a direction towards the pe- 

 riphery of the circle ; but, at the same time, it should 

 have descended as low as the level of the grate. It 

 should now enter the flue through a narrrow neck, 

 which extends through the whole periphery of the cir- 

 cle, and which opens into the flue all round. This 

 narrow aperture, which would be liable to be filled 

 with soot and the light ashes, should be provided with 

 a rake, which should work in the circumference of the 

 circle : Tin's being pushed, by a handle, to the right 

 and left, on the outside, from time to time, keeps the 

 circular neck clear. This long narrow aperture pre- 

 vents the rapid escape of the heated vapour, before the 

 heat is expended upon the vessel, and will be found 

 much superior to the plan of labyrinthal flues in econo- 

 mising fuel. From what has been observed, it will be 

 almost needless to suggest, that the greater the diameter 

 of the vessel to be heated, the more completely will the 

 vapour give out its heat, having, in this case, to make a 

 longer rout to get to the flue. Hence it will appear, from 

 this and other reasons, that the form of a still should be 

 such, that its diameter will admit of the greatest possible 

 quantity of heat being given out upon its bottom. Its 

 depth, at the same time, should be the least possible, in 

 order that the surface of the fluid may be as near as 

 possible to the source of heat. The economy of the fuel 

 will be still more increased, by having a double door to 

 the fire-place. The size of the fire-place should vary with 

 the quantity of liquid required to be distilled in a given 

 time. In the Scotch distilleries, where the duty is paid 

 for the time the still is employed, it is the interest of 

 the distiller to apply the heat in such a way, as to get 

 the greatest produce in a given time. It should be re- 

 collected, however, that this expedition is attended with 

 bad consequences, so far as regards the purity of the 

 spirit. When the ebullition is violent, which must be 

 the case in the expeditious way, there is greater risk of 

 the matter getting over in the liquid state to a certain 

 degree, by which the distilled product would be liable 

 to be contaminated We are informed, that in some of 



