_Insoluble Leaf._--The insoluble leaf as obtained in the determination of the extract, together with the weighed filter, is placed in an air-bath, and dried for at least eight hours at a temperature of 100°,[7] and then weighed. In genuine tea the amount of insoluble leaf ranges from 47 to 54 per cent.; in exhausted tea it may reach a proportion of 75 per cent. or more. It should be noted that in the foregoing estimations the tea is taken in its ordinary air-dried condition. If it be desired to reduce the results obtained to a dry basis, an allowance for the moisture present in the sample (an average of 6 to 8 per cent.), or a direct determination of the same must be made. The following tabulation gives the constituents of genuine tea, so far as the ash, extract, and insoluble leaf are involved:-- _Total ash_ ranges between 4·7 and 6·2 per cent. _Ash soluble in water_ ranges between 3 and 3·5 per cent.; should equal 50 per cent. of total ash. _Ash insoluble in water_, not over 3 per cent. _Ash insoluble in acid_ ranges between 0·3 and 0·8 per cent. _Extract_[8] ranges between 32 and 50 per cent. _Insoluble leaf_ ranges between 43 and 58 per cent. The table below may prove useful as indicating the requirements to be exacted when the chemist is asked to give an opinion concerning the presence of facing admixtures, or of exhausted or foreign leaves in a sample of tea. _Total ash_ should not be under 4·5 per cent. or above 7 per cent. _Ash soluble in water_ should not be under 40 per cent. of total ash. _Ash insoluble in water_ should not be over 3·25 per cent. _Ash insoluble in acid_ should not be over 1 per cent. _Extract_ (excepting in poor varieties of Congou tea) should not be under 30 per cent. _Insoluble Leaf_ should not be over 60 per cent. The British Society of Public Analysts adopt:-- _Total ash_ (dry basis), not over 8 per cent. (at least 3 per cent. should be soluble in water). _Extract_ (tea as sold), not under 30 per cent. Below are the proportions of total ash, ash soluble in water, and extract found in 850 samples of tea (mostly inferior and faced), examined under the direction of the author in the U.S. Laboratory:-- TOTAL ASH. ---------+--------+--------+--------+--------+-------+-------- Range |5 to 5½ |5½ to 6 |6 to 6½ |6½ to 7 |7 to 8 |8 p.c. | p.c. | p.c. | p.c. | p.c. | p.c. |and over Number | 21 | 76 | 102 | 194 | 421 | 36 Per cent.| 2·47 | 8·94 | 12·00 | 21·64 | 49·53 | 4·23 ---------+--------+--------+--------+--------+-------+-------- ASH SOLUBLE IN WATER. ---------+---------+----------+--------------+--------------- Range | Under 2 |2 to 3 per|3 to 3½ per |3½ per cent. |per cent.| cent. | cent. | and over. Number | 25 | 649 | 157 | 19 Per cent.| 2·94 | 76·35 | 18·70 | 2·23 ---------+---------+----------+--------------+--------------- EXTRACT.