142 ADULTERATION AND DETECTION. 



considerable percentage, usually averaging about 6 per 

 cent., so that a chemical examination of the ash forms an 

 important part of the analysis of tea. The proportion 

 of ash in all teas is tolerably constant, genuine tea rarely 

 yielding so little as 5 and never exceeding 6 per cent, of 

 ash on incineration. Therefore, to determine the amount 

 of ash, weigh a small quantity of the tea in its ordinary 

 commercial state and burn it in a platinum crucible and 

 then re-weigh the resultant ash ; by observing a few 

 simple precautions very constant and accurate results are 

 attainable by this method. The crucible should be clean 

 and bright, the lid fitting precisely; an iron triangle, 

 covered with a tobacco pipe may be employed to support 

 the crucible during ignition. The operation is then 

 commenced by igniting the empty crucible, and allowing 

 it to cool, being placed for that purpose on a piece of 

 porcelain or iron, immediately weighing the crucible on 

 becoming cold. Next place one or two grams of tea in 

 the crucible, weighing both together, and ignite over a 

 spirit lamp or good gas-burner, stirring the contents with 

 a platinum wire for a few minutes. When ignition is 

 complete the crucible is covered with the lid, let cool 

 again and immediately weighed a second time. If there is 

 any doubt as to the completeness of the ignition, the cru- 

 cible must be again ignited, and if there is no difference in 

 weight, the ignition is thereby proved finished. As is 

 obvious, in order to obtain accurate results it is 

 indispensable that the crucible should be in the 

 same condition when it is weighed empty and when 

 weighed with the ash, and this is insured by the 

 preliminary ignition and rapid re-weighing, as above 

 described. 



The following determinations of the percentages of 

 ash in spurious leaves most used in the adulteration of 



