DIYISIOK II. 



CHEMICALS REQUIRED FOR PHYTO-CHEMICAL 



ANALYSES. 



These cliemicals may be divided into — 



A. Absorbents. 



B. Solvents. 



C. Reagents. 



A. — Absorbents. 



These are principally: concentrated sulphuric acid, anhydrous 

 chloride of calcium and quicklime. 



They are used for drying a solid or liquid substance at 

 ordinary temperatiire and under exclusion of the air, by placing 

 them in a glass beaker close to the substance under the receiver 

 of an air-pump, and by working the latter occasionally after 

 intervals of two to three hours. 



Every one of the three substances named has its special value. 

 Eor quickness of action anhydrous lime is unsurpassed, and 

 especially so, when it has been reduced to about the size of peas; 

 but its power is soon exhausted, as it absoi'bs only 1 eq. water, 

 equal to ^ its own weight. Next in quickness acts concentrated 

 sulphuric acid, which absorbs up to 3 eq. water, increasing its 

 weight by one half. The slowest action is exercised by anhydrous 

 chloride of calcium, but though the least powerful yet it absorbs 6 

 eq. water or nearly its own weight, and besides it takes up another 

 quantity of water required to convert the compound Ca CI + 6 

 HO into the liquid state. 



By taking into account these different qualities, the choice of 

 the absorbent cannot be difficult. Should it be required to con- 

 duct the drying process as quickly as possible, quicklime is resorted 

 to; if less pressed for time, sulphuric acid; and if time is of no 

 consequence, chloride of calcium. [There may be other considera- 

 tions to guide in the choice of these absorbents.] 



