of reagents are those commonly employed; the concentration, however, need only be approximate: Acid Acetic 17 M Concentrated acetic acid, sp. gr. 1.064, containing about 96% CH3COOH Acid Citric 0.2 M 42 g. (CH2 COOH)2 C(OH) (COOH) · H2O made up to 1 liter Acid Formic 24 M Concentrated formic acid, sp. gr. 1.205 Acid Hydrochloric 12 M Concentrated HCl, sp. gr. 1.19-1.20 and containing about 39-40% HCl by weight Acid Hydrochloric 3 M Made by dilution of the 12 M HCl Acid Nitric 18 M Concentrated nitric acid, sp. gr. 1.42 and containing about 69% HNO, by weight Acid Sulphuric 18 M Concentrated sulphuric acid, sp. gr. 1.84 and containing about 97% H2SO4 by weight Ammonium Chloride 3 M 160.5 g. NH4Cl made up to 1 liter Ammonium Hydroxide 15 M Concentrated NH4OH, sp. gr. 0.90 and containing about 28% NH3 by weight Ammonium Hydroxide 3 M Ammonium Oxalate 0.25 M at 20-25° Made by dilution of 15 M NH4OH This is practically given by a saturated solution Barium Chloride 0.1 M 24.4 g. BaCl2 2H2O made up to 1 liter Potassium Sulphocyanate 0.1 M 9.7 g. KCNS made up to 1 liter di-Sodium Hydrogen Phosphate 0.25 M 89.5 g. Na2HPO·12H2O made up to 1 liter 26. Reagent Bottles. Every reagent bottle should always be kept scrupulously clean, particularly around the neck and mouth; a good plan is to have at hand a small, dampened, clean rag and wipe these parts carefully prior to using the reagent. The stopper should never be laid upon the desk, but should be held between the fingers or placed upon a clean watch-glass; and it should be returned immediately to its bott e as soon as the reagent has been withdrawn. All glass seems to be attacked more or less rapidly by the solvent action of solutions, particularly by alkaline solutions, and it is important to select the most resistant glass possible. One of the best glasses to be recommended for this purpose is the boro-silicate glass put out by the firm of Whithall-Tatum Co., New York, N. Y., under the trade name of "NonSol." 27. Distilled Water. Distilled water should be used in all analytical work, and in certain cases where the ordinary distilled water is not sufficiently pure, specially prepared distilled water (conductivity water) must be used. As generally prepared by boiling tap water and condensing the steam, distilled water is purified to the extent that most of the non-volatile constituents (NaCl, CaCO3, MgSO4 etc.) are left behind, but on the other hand the volatile constituents originally present in the water (i.e. ammonia, carbon dioxide) or generated during the distillation by the decomposition of the organic compounds or micro-organisms present (i.e. ammonia, volatile fatty acids, etc.) will be found to have passed over and be contained in the distillate. If the steam is condensed by means of a glass condenser, there will be a further contamination of the distillate due to the fact that steam has a marked solvent action upon glass. The best condenser to use is one made of pure block tin. It is hard to set any figures as to the amount of impurities in distilled water of one distillation because the amounts of impurities depend a lot upon the source of the tap water and the material of the condensing tube and somewhat upon the rate of distillation. In any event distilled water is far from being absolutely pure water. The following figures may perhaps be taken as indicative of what we may expect for distilled water prepared by the single distillation of a good potable water; the figures give the analysis of a sample of distilled water resulting from one distillation of New York City tap water from a continuous iron still with a block tin condenser; by way of comparison the impurities in the original tap water are given: 28. Conductivity Water. This is a name applied to distilled water of a very high degree of purity. For the preparation of conductivity water there are available several methods which are more or less elaborate, depending on the purity of the water desired; for the details of these the student is referred to the original articles. The following method, while not giving conductivity water of the utmost purity, is very satisfactory for many purposes and moreover is quite simple. One to two liters of distilled water are placed in a large round-bottomed flask having a capacity about twice the volume of water used. The flask is connected to a block tin condenser by means of a one-hole block tin stopper which is tapered and flanged at the top and bottom so that it can be wrapped with asbestos cord to serve as a packing. It is advisable to fit a small spray trap into the stopper. The trap is easily made by taking a piece of block tin tubing about three inches long, closing one end but providing the other end with a thread so it can be screwed into the stopper, and then drilling the walls with numerous tiny holes. The general arrangement is portrayed herewith in Fig. 3. After the water has been placed in the flask, a handful of glass beads is added to prevent subsequent bumping, then 50 c.c. of alkaline potassium permanganate solution containing 8 g. potassium permanganate and 300 g. potassium hydroxide per liter," and the distillation started. Affairs are now 5 Bourdillon, J. C. S. 103, 791 (1913). Kraus & Dexter, J. A. C. S. 44, 2468 (1922). The function of the alkaline permanganate is to decompose the nitrogenous and other organic substances (acids) present in the water. so adjusted that about 4 c.c. of water are condensed per minute while at the same time a small amount of steam is escaping at the exit end of the condenser. The first 300 c.c. of the condensate are rejected as this will contain ammonia; the succeeding portions of condensate are collected, until about one-quarter of the original water remains in the distilling flask when the distillation is stopped. Conductivity water rapidly becomes contaminated when stored in even the better grades of non-sol glass, so that only enough water should be prepared to take care of immediate needs. The following figures show the quality of conductivity water prepared by this method, starting with the distilled water mentioned in §27 and resorting to only one distillation from alkaline permanganate: 1. Calculate the quantities required to make up 100 c.c. of molar concentration of the following substances: KCl, Na2CO3 and FeCl3. 2. If each of the above solutions were diluted to 500 c.c., what would be their respective molarities? Ans. 0.2 M 3. If 1000 c.c. of copper sulphate solution was made by using 53.46 g. of CuSO4 5H2O what would be the molarity of such a solution? Ans. 0.214 M 4. How many c.c. of 18 M H2SO4 are required, so that when diluted to a liter, 5 c.c. will contain 0.49 g. of H2SO4? Ans. 55.5 c.c. 5. In 74 c.c. of solution of a certain salt, the molarity of which is 4.5, the salt content is 19.48 g. What is the formula weight of the salt? Ans. 58.4 g. 6. What is the molarity of a potassium permanganate solution of which 35 c.c. contain 0.770 g. KMnO1? Ans. 0.14 M 7. An analyst added 10 c.c. of 0.1 M silver nitrate solution to 15 c.c. of dilute hydrochloric acid, diluted with 200 c.c. of water, and obtained a precipitate of AgCl which weighed 0.0716 g. (complete precipitation assumed). What was the molarity of the hydrochloric acid? Ans. 0.033 M 8. In an analytical method for the separation of the Iron and Rare Earth Groups from manganese, nickel and magnesium, it is prescribed that a solution of ammonium chloride be used, the concentration of which is 5 g. of NH4Cl in 200 c.c. of solution. What is the molarity of this solution? Ans. 0.47 M 9. In the determination of ferric iron, according to Knecht and Hibbert, a titanous chloride solution is used, the strength of which is 1 percent TiCl. If the density of the solution at 20° were 1.005, what would be the molarity? Ans. 0.084 M 10. As a means of effecting the solution of a Type Metal alloy, it is recommended to use 15 c.c. of 12 M hydrochloric acid to a gram of sample, as the first step in the analytical procedure. How many grams of hydrogen chloride are contained in this amount of hydrochloric acid? Ans. 6.57 g. 11. The specific gravity of a certain sulphuric acid solution at 15°-15° is 1.810 and its percentage content of H2SO4 is 88.5%. How many c.c. of the acid must be diluted to 1 liter in order to give a resulting solution which shall be 6.0 molar? Ans. 367 c.c. 30. Apparatus for a Course in Quantitative Analysis. 4 Asbestos discs. 1 Banks generator. 2 Beakers, Pyrex, lipped, Griffins low form, 150 c.c. 1 Burette stand with porcelain base. 2 Burners, Tirrill, all brass. 1 Burner, Meker type. 2 Crucibles, porcelain, 25 c.c., with covers 1 Crucible, porcelain, Gooch pattern. 1 Crucible, iron, 60 c.c., with cover. 1 Crucible tongs, pair. 2 Casseroles, 11 cm. 1 Casserole, 16 cm. 1 Cork screw. 1 Desiccator, covered, 4", with quartz triangle fitted. 1 File, triangle. 1 Filter paper, package, acid washed, 9 cm. 1 Filter paper, package, acid washed, 121⁄2 cm. 5 Filter papers, 24 cm. 2 Flasks, Erlenmeyer, 250 c.c. 2 Flasks, Erlenmeyer, 500 c.c. 1 Flask, Erlenmeyer, heavy wall for filtering, 500 c.c. 1 Flask, graduated, flat bottom, G. S. 200 c.c. 1 Flask, graduated, flat bottom, G. S. 250 c.c. 1 Flask, graduated, flat bottom, G. S. 500 c.c. |