20 SUBSTJXCES SOLUBLE IX PETBOLEÜM SPIELT. 



for separating chlorophyll from the substances that accompany it. 

 But if series of analyses are to be made with the same plant, to 

 determine the changes it undergoes nnder the influence of the 

 seasons, or certain conditions of cultivation, etc., the relative 

 quantity of chlorophyll may be estimated by the optical (colori- 

 metric) method. It is better, however, to use alcohol or ether instead 

 of petroleum spirit, as the latter does not usually extract the whole 

 of the chlorophyll present. Admixture of foreign colouring matter 

 may be avoided by first extracting the material several times Avith 

 water, and drying the residue at the lowest temperature possible. 

 The chlorophyll may then be dissolved out by alcohol or ether. 

 (See further in §§ 37, 132.) 



Under the microscope chlorophyll is seen to be associated with 

 semi-fluid substances allied to protoplasm, often in the foim of 

 small granules (the so-called chlorophyll-gramdes), from which it 

 may be extracted by alcohol. It is more rarely found equally dis- 

 tributed throughout the Avhole of the protoplasm covering the 

 inner surface of the cell wall. It is bleached by chlorine and eau 

 de Labarraque ; the green colour is changed to yellow by dilute 

 acids, and blue by concentrated hydrochloric acid. 



§ 21. AllcaJokls extracted hy Petroleum S2)irif. — Parts of plants con- 

 taining alkaloid may, when extracted with petroleum spirit, yield 

 some of the alkaloid, together with fixed oil, to that menstruum, 

 even Avhen the pure alkaloid is insoluble in it. Here, too, it is the 

 fixed oil that determines the solution of the alkaloid. The jn-esence 

 of the latter may be detected by evaporating the petroleum-spirit 

 solution, shaking the residue with water acidulated with sulphuric 

 acid, and separating the aqueous from the oily liquid. Should an 

 emulsion have been formed, separation may be induced by allow- 

 ing the mixture to stand at a temperature of 40° to 50^ The 

 last traces of susjiended fat may be removed from the acid liquid by 

 shaking with petroleum spirit, and the presence of alkaloid demon- 

 strated by the usual reagents. (Cf. § G3.) The amount will not 

 often be large enough to cause a perceptil:)le error in the determi- 

 natioit of the fixed oil. But in dealing with very small quantities 

 of alkaloid tlie estimation of the latter may, under these circum- 

 stances, be appreciably aff"ected ; cases occur in which even the 

 whole of the alkaloid present passes into solution with the oil, 

 and would be overlooked if attention were not paid to this pro- 

 perty of fixed oil. On that account the petroleum-spirit solution 



