LECTURE XXVIIL 



CHEMISTRY; 



CHEMICAL APPARATUS. 



THE instruments used in chemistry may be 

 divided into three branches: 1st, The vessels 

 that hold the subjects on which the effect is to 

 be produced ; 2d, The apparatus for producing 

 heat ; 3d, The means of regulating or applying 

 heat in the best manner. 



Was it in our power, we should wish that the 

 vessels used in chemistry should possess the fol- 

 lowing properties : 1 st, Transparency ; 2d, The 

 property of resisting the action of corroding sub- 

 stances; 3d, The power of enduring sudden 

 changes of heat and cold; 4th, Strength, in order 

 to confine elastic vapour, &c.; and 5th, The 

 power of bearing great heat without melting. 

 But no matter in nature is possessed of all these 

 properties. The common materials are glass,, 

 metals, and earthen ware. 



1. The greatest inconveniency of glass vessels 

 is, that they do not well endure sudden changes 

 of heat and cold. It is the rule to make glasses 

 which are to bear heat as thin as possible, pro- 

 vided they are strong enough to be handled. 



