6 PRELIMINARY 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. If 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, 

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

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

 is advisable to allow the temperature to rise very gradually to 

 100 or 110. The greater part of the material can as a rule be dried 

 at 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 to 

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

 [ not require any preparation at all. It is very desirable 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 for 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 i 

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

 the amount of such volatile substances as may 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., 



ibicL Jg. 1869, p. 9. (Pharm. Journ. Trans. [2], xi. 84). In the 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. 



