6 PRELIMTNARY OPERATIONS. 



That portion which has served for the determination of the 

 moisture can subsequently be used for the estimation of the 

 total ash. 



§ 5. Treatment of Fresh Plants.— li fresh plants or parts of the 

 same are to be examined it will be advisable in. many cases, at 

 least if a quantitative examination is to be made, to first dry the 

 material, or it will at any rate be necessary for those portions 

 which are subsequently to be treated with petroleum spirit, ether, 

 -ilcohol, and similar menstrua. Here, too, it will be desirable to 

 nake an accurate estimation of the moisture, and in doing so it 

 s advisable to allow the temperature to rise very gradually to 

 1 00° or 1 10'. The greater part of the material can as a riJe be dried 

 a,t a temperature under, 30 till in a condition suitable for powder- 

 ing, and the amount of moisture still retained in.it can be deter- 

 mined in a small portion by a separate estimation. In drying 

 fleshy fruits or roots care should be taken not to. reduce them tx) 

 too fine a state of division.. Leaves which. are not too fleshy do 

 not require any preparation at alL It is very desirahle that as 

 little of the cell-tissue as possible should be deprived of its natural 

 covering, as by doing so the action of the air on the decomposable 

 constituents is only facilitated. With substances which are very 

 rich in sugar it is better not to dry the portions destined fqr the 

 estimation of the saccharine matter at all, but to examine, them in 

 the fresh state.. The same holds good for such substances as are 

 very rich in ethereal oil, or contain volatile acrid compounds ; 

 I shall subsequently show that such compounds may be easily 

 isolated from, and determined in, the fresh plants. Of course 

 the amount of such volatile substances as Uiay be found by other 

 means must be deducted from the result of the determination of 

 moisture. 



' §6. Powdering. — It is of the greatest importance that the 

 material for the various estimations should be uniformly mixed 

 and reduced to the very finest powder possible. It may be 

 asserted that the greatest errors made in the analysis of plants 

 are due to the material not having been reduced to a sufficiently 

 fine state of subdivision. Estimations of oil made with ether or 

 petroleum spirit often show differences of several units per cent., 



ibid. Jg. 1869, p. 9. (Fharm. Journ. Trans. [2], xi. 84). la tlie latter work 

 illustrations are given of the difference in composition that may be met with, 

 in fresh and dried, and in quickly and slowly dried, vegetable substances. 



