PHARMACY* 



employed. In choosing- the materials 

 for the construction of our ves- 

 properties most generally required ;u'C a 

 power of resist lit;- chemical agents, tran- 

 sparency, compactness, strength, fixity, 

 und infusibili y, and an ability to sustain 

 sudden variations of temperature without 

 breaking. 



Generally speaking, metals possess the 

 four last properties in considerable per- 

 fection ; but they are all opaque. Iron 

 arid copper are apt to be corroded by 

 chemical agents ; and a solution of the 

 last is often followed by dangerous affec- 

 tions. Tinning- them will sometimes, but 

 not always, answer ; for tin and lead are 

 often too fusible. Platinum, gold, and 

 silver, resist most of the chemical agents, 

 but are too expensive for general use. 



Good earthenware resists the greatest 

 intensity of heat, but has no other pro- 

 perty to recommend it. Clay, the basis 

 of all such wares, is plastic when worked 

 with water, and sufficiently hard when 

 burnt with an intense heat. But intense 

 heat contracts it unduly, and it is apt to 

 split and crack upon exposure to sudden 

 changes of temperature ; whence it is 

 necessary to counteract this property by 

 the addition of some other substance. 

 Siliceous sand, clay reduced to powder, 

 and then burnt with a very intense heat, 

 and plumbago, are occasionally used. 

 These additions, however, are attended 

 with other inconveniences ; plumbago 

 especially is liable to combustion, and 

 sand diminishes the compactness ; so 

 that when not glazed they are porous, 

 and when glazed they are acted upon by 

 chemical agents. The chemical vessels 

 manufactured by Messrs. Wedgewood 

 are the best of this description, except 

 porcelain, Which is too expensive. 



Glass possesses the three first quali- 

 ties in an eminent degree, and may be 

 heated red-hot without melting. Its 

 greatest inconvenience is its disposition 

 to crack or break in pieces when sudden- 

 ly heated or cooled. As this is occasion- 

 ed by its unequal expansion or contrac- 

 tion, it is best remedied by forming the 

 vessels very thin, and giving them, in ge- 

 neral, a rounded shape. Glass vessels 

 should also be well annealed, that is, 

 cooled very slowly, after being blown, by 

 placing them immediately in an oven 

 while they are yet in a soft state. When 

 ill annealed, or cooled suddenly, glass is 

 apt to fly in pieces on the slightest change 

 of temperature, or touch of a sharp point. 

 We may sometimes take advantage of 

 this imperfection ; for by means of a 



red-hot wire glass vessels may be cut into 

 any shape. Where there is not a crack, 

 already in the glass, the point of the 

 vivo is applied near the edge, by which a 

 crack is formed ; and this is afterwards 

 easily led in any direction we wish. 



Reaumur's porcelain is also glass, 

 which, by being surrounded with hot 

 sand, is made to cool so slowly that it as- 

 sumes a crystalline texture that destroys 

 its transparency, but imparts to it every 

 other quality desirable in chemical ves- 

 sels. The coarser kinds of glass are 

 commonly used in making it ; but as 

 there is no manufacture of this valuable 

 substance, its employment is still very 

 limited. 



Lutes also form a necessary part of 

 chemical apparatus. They are composi- 

 tions of various substances, intended to 

 close the joining of vessels, to cout glass 

 vessels, and to line furnaces. Lutes of 

 the first description are commonly em- 

 ployed to confine elastic vapours. They 

 should, therefore, possess the following 

 properties : viscidity, plasticity, compact- 

 ness, the power of resisting acrid va- 

 pours, and certain degrees of heat. The 

 viscidity of lutes depends on the pre- 

 sence either of unctuous or resinous 

 substances, mucilaginous substances, or 

 clay. 



Lutes of the first kind possess viscidity, 

 and resist acrid vapours in an eminent 

 degree ; but they are in general so fusi- 

 ble, that they cannot be employed when 

 they are exposed even to very low de- 

 grees of heat, and they will not adhere 

 to any substance that is at all moist. The 

 following are a few of this kind that have 

 been most frequently employed : 



Eight parts of yellow wax melted 

 with one of oil of turpentine, with or 

 without the addition of resinous sub- 

 stances, according to the degree of plia- 

 bility and consistence required. Lavoi- 

 sier's lute. 



Four parts of wax melted with two of 

 varnish and one of olive oil. Saussure's 

 lute. 



Three parts of powdered clay worked 

 up into a paste, with one of drying oil, 

 or, what is better, amber varnish. The 

 drying oil is prepared by boiling 22.5 

 parts of litharge in 16 of linseed oil, un- 

 til it be dissolved. Fat lute. 



Chalk and oil, or glaziers' putty, is wel! 

 fitted for luting tubes permanently into 

 glass vessels, for it becomes so hard that 

 it cannot be easily removed. 



Equal parts of litharge, quick-lime, and 

 powdered clay, worked into a paste with 



