362 Carholnjih-atcx of the Leaf of the Potato 



starch foiiud by the taka-diastase and the value found in this wa)' from 

 the rotation. 



The true starch in the leaf was estimated by treating with taka- 

 diastase the leaf material remaining after extraction with water ; this 

 was, of course, first gelatinised by boiling water in the usual way. 



The following is an actual example showing the method of analysis 

 and calculation. 



Potato Leaf, 8 p.m., July IGth, 1914. 



10-7148 grnis. of the dried powdered leaf material remaining after 

 the extraction of sugars^, dried at 110° in vacuo until the weight was 

 constant gave 9-8405 grms. ; the moisture present therefore = 8-16 

 per cent. 



The vacuum-dried weight of matter soluble in alcohol for this 

 picking was 59-:25 grms. 



The weight of oven-dried matter (fibre, starch), etc., left after 

 extraction with alcohol was 111-55 grms.; as the moisture in this was 

 8-16 per cent., the vacuum-dried weight = 102-42 grms. 



The total vacuum-dried matter (t.v.d.m.) therefore 



= 102-42 + 59-25 grms. = 161-67 grms. 



The 9-8405 grms. of leaf substance was transferred to a beaker 

 flask of 250 cc. capacity and left with about 200 cc. of water and 2 cc. 

 of toluene for 24 hours at 38°, stirring well at intervals. The clear 

 solution was then decanted through a starch-free filter paper as 

 completely as possible and the residue washed by decantation until 

 the volume in the flask was 250 cc. 



Aqueous extract. 50 cc. of the 250 cc. gave 0-0217 grm. CuO. 



Polarisation in 200 mm. tube = + 0-358° (sodium flame, 20°). This 

 rotation calculated as 100 grms. of vacuum-dried extracted leaf 



0-358 X 2-5 X 100 



9-8405 



9-10°. 



r. 1 1 ^ 1 ^nr^ r 9-10x102-42 _ __„ 



Calculated on 100 grms. of t.v.d.m. = = 5-76 . 



161-67 



Calculated as soluble starch ([a]„ = 202°) per 100 grms. of t.v.d.m. 



_ 0-358 X 2-5 x 10« x 1 02-42 



~ 2 X 202 x 9-8405 x 161-67 ~ P*"'' '^'^"*- 



• This had been dried in an oven at 100°, ground in a mill and kept in a stoppered 

 bottle until the analysis was made. For precautions in sampUng this material see Davis 

 and Daish [1914], p. 161. 



