that, because of the present scarcity and high price of potash, it might be desirable for the association to make a further study of the subject with a view to adopting some modification of the present official method applicable to ashes and cement potash products. REPORT ON WATER. By J. W. SALE (Bureau of Chemistry, Washington, D. C.), Referee. Three analytical methods were selected for the cooperative work, a rapid method for the determination of calcium and magnesium; a method for barium; and one for manganese. Numerous tests on the determination of free ammonia in water containing hydrogen sulphid were also conducted. This latter work was done in the Bureau of Chemistry, principally for the reason that sulphid waters change so rapidly in composition that it is not practicable to forward standard samples to collaborators. Three samples of solutions of known composition, together with copies of the proposed methods, were forwarded to each of the collaborators. The methods of analysis, composition of standard samples, and results of the cooperative work are given below. The methods of analysis, submitted herewith, have been slightly modified to make them of general application. INDUSTRIAL WATER. REAGENTS. (a) Standard potassium permanganate solution, approximately N/5.—Dissolve 6.322 grams of pure crystals in water and make up to 1 liter. Standardize against pure Iceland spar by the procedure given below. (b) Standard sodium thiosulphate solution, approximately N/5.—Dissolve 49.6 grams of recrystallized sodium thiosulphate in 1 liter of water. Standardize against magnesium ribbon or some suitable compound of magnesium by the procedure given below. (C) Ammonium arsenate, crystals. (d) Oxalic acid, crystals. (e) Potassium iodid, crystals. (f) Sulphuric acid (1 to 1). DETERMINATION1. Acidify and concentrate the sample as usual. Add about 0.5 gram of ammonium chlorid and precipitate the iron and alumina with ammonium hydroxid. Boil, filter and wash. To the filtrate, in a volume of about 100 cc., add 0.5 gram of oxalic acid, together with sufficient hydrochloric acid to clear the solution. Add 1-2 drops of methyl orange, heat to boiling and make slightly alkaline with dilute ammonia. Add immediately sufficient ammonium arsenate to precipitate the magnesium, then slowly add ammonia, with constant stirring, to the hot solution until the magnesium am 1 J. Ind. Eng. Chem., 1913, 5: 910. monium arsenate comes down, or if the calcium oxalate is present in such quantity that this can not be observed, add about 10 cc. of strong ammonia water. Let cool and add 10-15 cc. more of strong ammonia. Let stand for 30 minutes with frequent shaking, filter and wash thoroughly with dilute ammonia water. Transfer the precipitate to a 300-500 cc. Erlenmeyer flask, using dilute sulphuric acid and water. Add 10 cc. of sulphuric acid, make up to about 75-80 cc. and titrate hot with permanganate solution. Let cool and add 25 cc. more of the acid. Add slowly 5 grams of potassium iodid and immediately titrate to a straw color with sodium thiosulphate. Stopper the flask and cover with black paper, or set in the dark for about 5 minutes. Eight minutes should elapse between the addition of the iodid and the last part of the titration. Without adding starch, complete the titration drop by drop. Read the end point and place the flask in the dark for 1 minute. If there is a return of color, discharge it. Usually there will be none if the last drops of thiosulphate have been added slowly. Apply a correction for iodin set free by the light, etc., by titrating as described above with 10 cc. and 20 cc. of a solution of ammonium arsenate (of which the exact concentration need not be known-about 20 grams to a liter is convenient). If 10 cc. required cc. of thiosulphate and 20 cc. required y cc., then the correction is (2x - y) cc. MANGANESE. (a) Dilute nitric acid (1 to 4).-Free from brown oxid of nitrogen by aeration. (b) Sulphuric acid (1 to 3). (C) Dilute sulphuric acid.-Dilute 25 cc. of concentrated acid to 1 liter with distilled water. Add enough permanganate solution to color faintly the dilute acid. (d) Standard manganous sulphate solution.-Dissolve 0.2877 gram of pure potassium permanganate in about 100 cc. of distilled water, acidify the solution with sulphuric acid and heat to boiling. Add slowly a sufficient quantity of a dilute solution of oxalic acid to discharge the color. Cool and dilute to 1 liter. One cubic centimeter of this solution is equivalent to 0.1 mg. of manganese. The standard should be prepared by following the same procedure as is used for the sample. This solution is more permanent than a solution of potassium permanganate, which may, however, be used. To prepare it, dissolve 0.288 gram of potassium permanganate in distilled water and dilute the solution to 1 liter. (e) Sodium bismuthate.-Pure dry salt. DETERMINATION. Remove chlorin by two or more evaporations with sulphuric acid from such a quantity of the sample as contains 1.0 mg. or less of manganese. Volatilize the sulphuric acid and ignite the residue gently at less than 500°C. Dissolve in 40 cc. of nitric acid, add about 0.5 gram of sodium bismuthate, and heat until the permanganate color disappears. Add a few drops of a solution of ammonium or sodium bisulphate to clear the solution and again boil to expel oxids of nitrogen. Remove the solution from the source of heat, cool to 20°C., again add 0.5 gram of sodium bismuthate, and stir. When the maximum permanganate color has developed, filter through an alundum or Gooch crucible containing an asbestos mat which has been ignited, treated with a solution of potassium permanganate and washed with distilled water. Wash the precipitate with dilute sulphuric acid until the washings are colorless. Transfer the filtrate to a colorimeter tube and compare the color of it with that of standards prepared from the potassium permanganate solution. To prepare the standards, dilute with sulphuric acid, (C), portions of 0.2, 0.4, 0.6 cc., etc., of the permanganate solution to the same volume as the filtrate. BARIUM. REAGENTS. (a) Ammonium dichromate solution.-One hundred grams to the liter. (b) Ammonium acetate solution.—Three hundred grams, neutralized by ammonia, to the liter. (C) Ammonium acetate solution.-Twenty cubic centimeters of (b) diluted, to 1 liter. Reaction of acetate solution should be alkaline rather than acid. DETERMINATION. By weighing as barium chromate. Acidify and concentrate the sample as usual. Add about 0.5 gram of ammonium chlorid and precipitate the iron and aluminium with ammonium hydroxid. Boil, filter and wash. To the filtrate add ammonium acetate [10 cc. of (b)] in excess (volume about 200 cc.). Heat to boiling and add, with stirring, about 5 cc. of the dichromate solution, (a). Allow to settle and cool. Decant the clear liquid through a filter, wash the precipitate by decantation with ammonium acetate, (C), until the filtrate is no longer perceptibly colored, which will require about 100 cc. of wash solution. Place the beaker under the funnel, dissolve the precipitate on the paper with warm dilute nitric acid, using as little as possible, and wash the paper. Add a little more acid to dissolve the precipitate in the beaker, follow with ammonia until the precipitate forming again no longer redissolves. Heat to boiling, add, with stirring, ammonium acetate [10 cc. of (b)], and ammonium dichromate solution [2 cc. of (a)], allow to cool slowly and wash the precipitate by decantation with (C). Dry the barium chromate, burn the filter separately, ignite moderately to constant weight. Weigh as BaCrO4. By titration. * wash the precipitate by Proceed as in the method just described to decantation with (C)", then proceed as follows: Dissolve the precipitate in about 10 cc. of a mixture of hydrochloric acid (1 to 1) and hot water. Wash the filter and dilute the solution to about 400 cc.; add about 50 cc. of a freshly prepared 10% solution of potassium iodid. Mix carefully and titrate the liberated iodin after 3-4 minutes with standard thiosulphate (1 cc. of N/10 thiosulphate = 4.579 mg. of barium). = † Manganese present in the form of sulphate; other bases present in the form of chlorids. In considering the results on calcium and magnesium, it should be borne in mind that this method was selected as a rapid volumetric method for use in examining waters for industrial purposes and as a possible substitute for the so-called soap method. Extreme accuracy in this method may be sacrificed if rapidity and reasonable accuracy are attained. The comments of the collaborators, with one exception, indicate that the method is worthy of consideration and that the results submitted, with the exception of one set of magnesium determinations, are sufficiently close to theory, considering the field in which the method is to be used. The remarkably low results on magnesium in the one instance may have been caused by adding an insufficient amount of ammonium arsenate reagent to precipitate all of the magnesium, by a too prolonged washing of the mixed precipitate, or by using an incorrect value for the standard thiosulphate solution. If the low results are due to either of the first two reasons suggested, the method could be changed by stating the minimum amount of arsenate reagent to be added, say 2-3 grams, as suggested by one of the collaborators, and by cautioning against prolonged washing of the mixed precipitate. In the referee's opinion, the indefiniteness of the end point in titrating the iodin with standard thiosulphate is the fundamental criticism to be made of the method. If this objection can not be overcome, the method should not be adopted. However, it is believed that very fair results can be obtained if the directions given regarding the titration are closely followed. With regard to the use of Iceland spar, the following directions were forwarded to the collaborators on July 17, 1917: It appears that Iceland spar is not always available for the standardization of the potassium permanganate solution in the determination of calcium. Furthermore, it has been found to contain impurities which may vitiate the results. It is suggested, therefore, that the phrase "or some suitable compound of calcium" be inserted in the third line under "Reagents (a)” after “* pure Iceland spar". The referee does not feel warranted, in view of the data at hand, in recommending the adoption of this method until further cooperative work has been done upon it. It is suggested, however, that it be revised as indicated above and that the referee for 1918 be instructed to give it further consideration. The methods for barium and for manganese tested this year, unlike the volumetric method for calcium and magnesium, are old, well-tested methods, in general use. The results on barium obtained by igniting the precipitate are generally slightly low, due probably to reduction of the precipitate on ignition and to the solubility of the barium chromate precipitate in the wash water. The following results, obtained by titrating the precipitate, were sent in by the collaborators: When it is considered that some of the analysts used this method for the first time, the results obtained are quite satisfactory. The results on manganese by the well-known sodium bismuthate method are very satisfactory. It seems probable that even better results would have been obtained if the portions taken for analysis had contained less manganese. A milligram of manganese, in the form of potassium permanganate in 50 cc. of solution, gives a color that is too deep |