PHARMACY. 



oil varnish, is sometimes used to daub 

 over the cracks in glass vessels, so as to 

 render them again fit for some purposes. 



Melted pitch and brick dust. 



Mucilaginous substances, such as flour, 

 starch, gum, and glue mixed with water, 

 with or without some powder, are suffi- 

 ciently adhesive, are dried by moderate 

 degrees of heat, and are easily removed 

 after the operation, by moistening them 

 with water. But a high temperature de- 

 stroys them, and they do not resist cor- 

 rosive vapours. Of these take the fol- 

 lowing forms : 



Slips of bladder macerated in water, 

 and applied with the inside next the ves- 

 sels. They are apt, however, from their 

 great contraction on drying, to break 

 weak vessels. 



One part of gum arabic with six or 

 eight of chalk, formed into a paste with 

 water. 



Flour worked into a paste with pow- 

 dered clay er chalk. 



Almond or linseed meal formed into a 

 paste with mucilage or water. 



Quicklime in fine powder, hastily mix- 

 ed with white of egg, and instantly ap- 

 plied, sets very quickly, but becomes so 

 hard that it can scarcely be removed. 



Slaked lime in fine powder, with gliie, 

 does not set so quickly as the former. 



The cracks of glass vessels are some- 

 times mended by daubing them and a 

 suitable piece of linen over with white 

 of egg, strewing both over with finely 

 powdered quick lime, and instantly ap- 

 plying the linen closely and evenly. 



Earthy lutes resist very high tempera- 

 tures, but they become so hard that they 

 can scarcely be removed, and often hard- 

 en so quickly after they are mixed up, 

 that they must be applied immediately. 

 Examples : 



Quick-lime well incorporated with a 

 sixth part of muriate of soda. 



Burnt gypsum, made up with water. 



One ounce of borax dissolved in a 

 pound of boiling water, mixed with a suf- 

 ficient quantity of powdered clay. Mr. 

 Watts's fire lute. 



One part of clay with four of sand form- 

 ed into a paste with water. This is also 

 used for costing glass vessels, in order to 

 render them stronger, and capable of re- 

 sisting violent degrees of heat. It is then 

 jmade into a very thin mass, and applied 

 in successive lay ers, taking; care. that each 

 coat be perfectly dry before another be 

 laid on. 



The lutes for lining furnaces will be de- 

 scribed .-hen treating of furnaces. 



The junctures of vessels which are to 

 be luted to each other, must previously 

 be accurately and firmly fitted, by intro- 

 ducing between them, when necessary, 

 short bits of wood or cork, or, if the dis- 

 proportion be very great, by means of a 

 cork fitted to the one vessel, having a cir- 

 cular hole bored through it, through 

 which the neck of the other vessel or tube 

 passes. After being thus fitted, the lute 

 is either applied very thin, by spreading 

 it on slips of linen or paper, and securing 

 it with thread, or, if it is a paste lute, it i* 

 formed into small cylinders, which are: 

 successively applied to the junctures, 

 taking care that each piece be made to 

 adhere firmly and perfectly close in every 

 part, before another is put on. Lastly, 

 the whole is secured by slips of linen or 

 bladder. In many cases, to permit the 

 escape of elastic vapours, a small hole is 

 made through the lute with a pin, cr the 

 lute is perforated by a small quill, fitted 

 with a stopper. 



Heat and Fuel. As caloric is an agent 

 of the most extensive utility in the chemi- 

 cal operations of pharmacy, it is necessa- 

 ry that we should be acquainted with the 

 means of employing it in the most econo- 

 mical and efficient manner. The rays ot" 

 the sun are used in the drying of many 

 vegetable substances, and the only atten- 

 tions necessary are to expose as large a 

 surface as possible, and to turn them fre- 

 quently, that every part may be dried 

 alike. They are also sometimes used for 

 promoting spontaneous evaporation. 



The combustion of different substances 

 is a much more powerful and certain, 

 source of heat. The substances employ- 

 ed for this purpose, are either fluid or 

 solid. Alcohol, oil, tallow, wood, turf, 

 coal, charcoal, and coke, are ail occasion- 

 ally employed. Alcohol, oil, and melted 

 tallow, fluid inflammables, must be burnt 

 on porous wicks. These act merely me- 

 chanically, by drawing up a portion of the 

 fluid to be volatilixed and inflamed. They 

 are therefore burnt in lamps of various 

 constructions. But although commonly 

 used to produce light, they afford a verf 

 uniform, though not very high tempera- 

 ture : it may, however, be increased by 

 increasing the number of the wicks, and 

 their size. Alcohol produces a steady 

 lieat, no soot, and, if strong, leaves no re- 

 siduum. Oil gives a higher temperature, 

 but on a common wick produces much 

 smoke and soot. These are diminished, 

 and the light and heat increased, by mak- 

 ing the surface of the fltxme bear a large 

 proportion to the centre, which is best 



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