266 The VarboUiidiatcs of the MaiujuUl Leaf 



For actual examples of the method of calculation see Appendix, 

 pp. 31Dto 319. All results are calculated as a percentage on the total 

 vacuum-dried mailer of the leaf (t.v.d.m.), that is on the sum of the 

 alcohol-sohil)le and alcohol-insoluble substances. 



Extraction of the sugars from the leaf material and preparation of the 

 solution for analysis. The freshly plucked leaf material (about 1 kilo- 

 gram) was cut off close at the end of the stalk and, after cutting out 

 the mid-ribs, was dropped, in small quantities at a time, into two litres 

 of boiling 95 per cent, alcohol to which 20 cc. of 0-880 ammonia had 

 been added, contained in a large zinc beaker (14 ins. x 9 ins.) in which 

 the alcohol could be safely boiled ; after each addition, the whole mass 

 was well stirred so as to immerse the newly added leaves and ensure the 

 rapid destruction of the enzymes. The whole kilogram of leaf could 

 be added in less than 10 minutes; the time of picking each sample 

 was also about 10 minutes, the picking being commenced 5 minutes 

 before the hour and completed 5 minutes after. As the Laboratory 

 was near at hand, the w-hole mass of leaf could be added to the 

 boiling alcohol in less than 30 minutes from the nominal time of 

 picking. The stalks and "mid-ribs were separately dropped into a 

 smaller (juantity of boiling alcoiiol (1 litre containing 10 cc. of 0-880 

 ammonia) contained in a smaller zinc vessel (12 ins. x 5 ins.). After 

 the leaf or stalk material had been added to the alcohol, the latter was 

 kept boiling about half-an-hour; the alcohol was then drawn oft' and 

 transferred to the boiling vessel B of a large specially constructed 

 zinc extraction apparatus, shown in Fig. P. The leaf material was 

 packed into the extraction vessel A, which was fitted with a detachable 

 false bottom of perforated zinc and acted on the principle of the ordinary 

 Soxhlet extractor, the alcohol siphoning back from A into the boiling 

 vessel B during the extraction. B was heated by a large water-bath. 

 Two condensers were fitted at the top of the extractor to condense the 

 alcohol vapour which was conveyed from the boiling vessel by a bent 

 tube of compo-metal so arranged that it could be easily fitted to or 

 disconnected irom the ap])aratus, through the corks of which it passed. 

 This tube and tlie extractor itself were wrapped in felt to minimise 

 air-cooling. The extraction was generally complete after about 12-18 

 hours; preliminary experiments showed that the whole of the sugars 

 are removed when the leaf becomes colourless. To hasten the extraction, 

 the leaves should be turned out of the extractor after about 1(1 hours 



' For the mid-ribs and .stalks a smaller extraction apparatus of zinc was used. The 

 dimensions of vessel A were 7" x 4" and of B 5" x 5", with a 2" neck. 



