A system of instruction in quantitative chemical analysis / by C. Remigius Fresenius.
- Fresenius, C. Remigius, 1818-1897. Anleitung zur qualitativen chemischen Analyse. English
- Date:
- 1854
Licence: Public Domain Mark
Credit: A system of instruction in quantitative chemical analysis / by C. Remigius Fresenius. Source: Wellcome Collection.
529/680 page 509
![filtcred through animal cliarcoal, the precipitate tlioroughly washed, and the washings added to the filtrate, which is then diluted to ten, fifteen, or twenty times its original bulk (Neubauer). c. Cane sugar, or vegetable juices containing cane sugar (the juices of the sugar cane, beetroot, maple, &c.), must first be converted into grape sugar. This is effected by protracted beating witb dilute sulpburic acid. Tlius, for instance, to prepare beetroot juice for the quantitative estimation of the saccharine matter contained in it, take from 15 to 20 c. c. of the juice treated as directed in b., add twelve drops of dilute sulpburic acid (S03, HO+ 5 water), and boil the mixture from one to two hours, adding water as it evaporates; this Operation is conducted best on a water-batb. Neutralise tlie free acid bymeans of a dilute solution of car- bonate of soda, dilute to ten times the original volume, and examine the fluid as directed in 1. 100 parts of grape sugar (C12H12012) correspond to 95 parts of cane sugar (C12HuOu). Accordingly, it takes 0-0-175 grm. of cane sugar to decompose 10 c. c. of the copper solution. d. Starch and dextrine, or substances containing either of these bodies, are treated in the same way, but the action of the sulpburic acid is con- tinued much longer than in the conversion of cane sugar into grape sugar. For instance, to convert 1 gramme of starch into grape sugar, proceed as follows: mix the gramme of starch witb ] 0 grammes of water, shake the mixture, apply heat, still shaking, until a paste is formed; add to this 12 drops of dilute sulpburic acid (1 to 5), and apply heat until the fluid becomes thin, boil the fluid now from 6 to 10 hours in an ob- liquelv placed flask on the sand-bath, frequently replacing the evapo- rated water ;* or heat the fluid from 24 to 36 hours in the water- bath. When the conversion into grape sugar is completed, dilute the fluid to 100 or 200 c. c., and proceed as directed in 1. The reaction witb tincture of iodine, which bas been proposed by several chemists, as a test to ascertain whether the conversion into grape sugar is completed, is not suflficiently reliable. To remove all doubt heat 20 c. c. of the fluid again for several hours, rinse into a measuring tube, dilute to 40 c. c., and pro- ceed again as directed in 1. This second experiment must take exactly double the quantity of solution of copper used in the first; if less is required, this is a proof that an additional quantity of sugar has been formed upon the renewed application of heat.f * The Operation may be greatly facilitated by closing the flask with a perforated cork furnished with a glass tube bent at an obtuse angle, and which leads to a cooling apparatus tumed upwards; by this arrangement the evaporating water returns to the flask. f The complete conversion of starch into sugar may be effected also by making the starch into paste, and digesting this for several hours, at a temperature of from 140° to 158°, with a measured quantity of infusion of malt. If the sugar is now determined in an](https://iiif.wellcomecollection.org/image/b28133742_0529.jp2/full/800%2C/0/default.jpg)
