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.
509/680 page 489
![ANALYSIS OF COMMON SALT. § 199.] is clearly seen from the changed color of the solution.)* Dilute now the contents of the dish with water, filter, wash, dilute to about 250 c. c., and acidify with hydrochloric acid. This produces a strong white turbidity caused by the Separation of ferrocyanide of lead. Disregarding this, add the solution of permanganate of potassa. The precipitate dissolves in proportion as the conversion of the ferro- cyanide into ferricyanide ensues, and the termination of the reaction is thus distinctly indicated, not only hy the change of color, hut also by the perfect clearness of the fluid.f Of various methods employed to reduce the ferricyanide of potassiunq none were so accurate as this. Repeated experiments gave perfectly satisfactory results. The only thing to be observed is that the fluids must be concentrated. Lastly, to analyse a substance, containing both ferro- and ferricyanide of potassium, prepare the solution as directed, and then examine one portion of 10 c. c. at once, and another portion of 10 c. c. after previous reduction. The first process gives simply the amount of ferrocyanide of potassium contained in the analysed salt, the second gives this together with the quantity of ferrocyanide formed from the ferricyanide originally present in the analysed salt. Now, astwo equivalents of crystallised ferrocyanide of potassium = 5281 correspond to one equivalent of ferricyanide of potassium = 4117, the quan- tity of the latter is found by multiplying by 0-7/95, the difference between the results of the two processes, expressed as crystallised ferrocyanide of potassium. The reaction on which this method is based ensues in the manner shown in the following equation: 10 (Cfy, 2 H) + Mn2 07-f2 I1C1 = 5 (2 Cfy, 3 H) + 2 Mn CI + 7 HO. This has been proved by direct experiments. The results are very accurate. 6. Analysis of common salt. § 199. I select this example to show how to analyse with accuracy and tolerable expedition, salts which, with a predominant principal ingredient, contain small quantities of other substances. a. Reduce the salt by trituration to a uniform powder, and put this into a stoppered bottle. * Actual ebullition, more especially continued for any length of time, should be avoided, as it tends to cause the solution of a large proportion of oxide of lead, which would in some measure interfere with the ulterior process. f As ferrocyanide of lead in not altogether insoluble, but simply difficultly soluble in a hydrochloric acid fluid, the fluid first becomes clear, and then only after addition of a few more drops, x-eddish-yellow. It is the latter point which must be attained before the reaction can be considercd complete.](https://iiif.wellcomecollection.org/image/b28133742_0509.jp2/full/800%2C/0/default.jpg)
