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In Crown 8vo. Pp. i-viii + 194. With Diagrams. 45. net. ELEMENTARY PRACTICAL CHEMISTRY. For Medical and Other Students. By J. E. MYERS, M.Sc., and J. B. FIRTH, M.Sc. CONTENTS.-PART I. General Methods of Manipulation, and Preparation of Substances. PART II. Qualitative Analysis. PART III. Quantitative Analysis. PART IV. Organic Analysis APPENDICES. INDEX. "Deals clearly with the principles upon which all work, whether elementary or advanced, must be firmly grounded."-Chem. Trade Fnl. London: C. GRIFFIN & CO., Ltd, Exeter Street, Strand.

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THE QUALITATIVE ANALYSIS OF THE IRON GROUP IN PRESENCE OF PHOSPHATES. By ROBERT GILMOUR.

Two general methods for the separation of the metals of the iron group are in common use. In the first of these iron, aluminium, and chromium are separated as hydroxides by means of ammonia in the presence of ammonium chloride, and the filtrate is treated with ammonium sulphide, which precipitates the remainder of the metals of the group as sulphides. In the second method the metals are precipitated together as hydroxides and sulphides by the addition of ammonia, ammonium chloride, and ammonium sulphide. The subsequent isolation and identification of the constituent metals may then be effected by several methods, each of which possesses certain advantages, but all of which possess also serious disadvantages.

The separation of iron, chromium, and aluminium by precipitation with ammonia is never an entirely satisfactory process, since manganese is certain to be partially precipitated at the same time, unless a large excess of ammonium chloride is present, and even then oxidation of the manganese salt to the manganic state, through absorption of atmospheric oxygen and subsequent precipitation along with the iron, chromium, and aluminium, is sure to occur to some extent. Again, a considerable quantity of zinc may be precipitated if much chromium is present, and manganese, zinc, and nickel may all be carried down in presence of much iron (Noyes, Journ. Am. Chem. Soc., 1908, xxx., 482). Furthermore, as will be shown later, magnesium may be carried down almost completely if much aluminium is present, unless a much larger amount of ammonium chloride has been added than is usual in qualitative analysis. With regard to the separation of the remaining metals of the groups, the chief difficulty is the solubility of nickel sulphide in yellow ammonium sulphide. This can be overcome, however, by precipitating with hydrogen sulphide in ammoniacal solution (loc. cit.).

When the metals are precipitated together as hydroxides and sulphides the above mentioned difficulties do not, of course, occur, except that magnesium may be precipitated in presence of much aluminium. When, however, we come to consider the further separation of the metallic radicles of this group fresh difficulties appear. Many textbooks recommend treatment of the precipitated hydroxides and sulphides with cold dilute hydrochloric acid in order to separate the insoluble nickel and cobalt sulphides from the remaining metals of the group, but this is far from satisfactory, for, as Thiel and Gessner have shown (Zeit. Anorg. Chem., 1914, lxxxvi., 1), nickel sulphide when

precipitated under ordinary qualitative conditions is soluble to a very considerable extent in o'5/N or even o'1/N hydrochloric acid, due to the probable existence of three distinct forms of the sulphide, which vary in solubility; consequently, the separation is very incomplete. Another difficulty, which does not seem to have been mentioned in the literature, occurs when a phosphate is present along with metals of the alkaline earth group in the solution undergoing examination. In the usual analytical schemes iron and phosphate are separated together by the basic acetate process, leaving manganese, barium, strontium, calcium, and magnesium in solution, and also nickel and cobalt if these have not been separated previously. This process is not without its drawbacks, for it has been found that barium may be almost completely precipitated along with the ferric phosphate and basic ferric acetate, and strontium and calcium to a considerable extent. Consequently, if all the barium has come down with the iron group on account of a large amount of phosphate being present it may be missed altogether, since the ferric phosphate precipitate is generally neglected. This seems to add another charge to the already long list against the method of separating the alkaline earths as carbonates after the iron group, and constitutes another argument in favour of Curtmann and Marcus's method of separating them as sulphates after the silver group (Journ. Am. Chem. Soc., 1912, xxxiv., 1493), or after the copper group as advocated in this paper. Certainly one or other of the methods must be adopted if the separation is to be at all exact, and it is largely a matter of choice which one, for on the one hand, if the sulphates are precipitated before the copper group it is necessary to treat them with ammonium acetate to remove lead, while on the other hand precipitation of the sulphates after removal of the copper group may result in a certain loss of barium, particularly if ferric chloride or other oxidising agent happens to be present. On the whole, the method of Curtmann and Marcus is perhaps to be preferred from the point of view of accuracy. Care must be taken, however, to make the separation of the sulphates as complete as possible by the addition of a considerable quantity of alcohol, for the scheme about to be described gives little further opportunity for the detection of the alkaline earth metals if a phosphate is present.

In consequence of the difficulties which have been referred to above an attempt has been made to devise a more satisfactory working method for the analysis of the iron group, and this has been more or less successfully accomplished.

The scheme taken in conjunction with those already advocated for the analysis of the copper and alkaline earth groups (CHEMICAL NEWS, 1915, cxi., 206 and 217) con

Briefly the procedure is as follows:

The solution from which the metals of the silver and copper groups have been eliminated is boiled to remove H2S. The alkaline earths are then removed as sulphates by means of H2SO4 and alcohol. The precipitated sulphates are converted into carbonates and analysed according to the method previously described in this journal (loc. cit.).

The filtrate is heated on the water-bath for some time to remove alcohol, NaOH is added, and then Na2O2 in considerable quantity. The mixture is boiled for some minutes and filtered. The filtrate contains aluminium, chromium, and zinc, and most of the phosphate if this is present. The precipitate contains Fe(OH)3, Ni(OH)2, Ni(OH)3, MnO(OH)2, Co(OH)3, Mg(OH)2, and phosphates of these. The filtrate is examined as usual for Al, Cr, and Zn. The precipitate is dissolved in HCl, and the solution evaporated to dryness. The residue is taken up in water, tested for iron, and Fe and phosphate removed by the basic acetate process. The filtrate contains Ni, Co, Mn, and Mg. It is heated to boiling, and H2S is passed in. Ni and Co are precipitated as sulphides. The filtrate is made alkaline with NH4OH, and H2S again passed in; Mn is precipitated as sulphide. The filtrate on addition of (NH4)2HPO4 gives Mg as MgNH,PO4.

Na and K are tested for in a portion of the original solution after removing all other metals by means of NH4OH, NH4Cl, H2S, and (NH4)2C03.

1. To a solution containing 56 mgrms. of Al and 64 mgrms. of Zn as chlorides, 2 cc. of 2/N (NH4)2HPO4 were added, then NaOH until the precipitate just dissolved. A pinch of Na2O2 was then added and the solution boiled. A white granular precipitate came down, which would not dissolve on continued boiling.

2. In a similar experiment, in which the Na2O2 was omitted, the same white granular precipitate was obtained.

3. Solutions containing 56 mgrms. of Al and 64 mgrms. of Zn were treated with NaOH until clear. On boiling the solutions they remained clear, but on mixing them and boiling the white precipitate appeared.

4. 500 mgrms. of ZnSO4, 500 mgrms. of Al2(SO4)3, and 500 mgrms. of (NH4)2HPO4 were dissolved in NaOH solution. A quantity of Na2O2 was added and the solution boiled. Only a small amount of the white precipitate appeared.

A further series of experiments of a similar nature showed that if the amount of NaOH or Na2O2 which was added was considerably in excess of that required to dissolve the precipitated hydroxides, then no insoluble substance was formed, whereas if only a sufficient amount was present to just dissolve the hydroxides when precipitated in separate solutions, or a very small excess over this amount, then on boiling the white precipitate was formed. This result would seem to point to the formation of some compound containing Zn and Al, possibly zinc aluminate, and on this assumption might be regarded as due to an equilibrium reaction, with_NaAIO2 and Na2ZnO2 on one side of the equation and zinc aluminate and NaOH on the other side. An excess of NaOH would thus tend to prevent the formation of the zinc aluminate, inasmuch as it would facilitate the ionisation of both zinc and aluminium hydroxides in the acid form.

The experiments show clearly, at any rate, that a considerable excess of Na2O2 is required in the peroxide separation of Al, Cr, and Zn, as otherwise appreciable quantities of Zn and Al may remain undissolved, along with CO, Ni, and the other metals of the group.

excess.

by means of NH4OH.

1. To a solution containing 56 mgrms. of Al as chloride and 48 mgrms. of Mg as sulphate in 30 cc. about 2 grms. of solid NH4Cl were added, and then NH4OH in slight The mixture was boiled and filtered and the precipitate (a) well washed. The filtrate gave on adding (NH4)2HPO4 a precipitate of MgNH,PO4 (b).

The precipitate (a) was dissolved in dilute HCl, 1 grm. of NH4Cl and excess of NH4OH were then added and the mixture boiled.

The precipitate was filtered off and washed (c). The filtrate gave a small precipitate with (NH4)2HPO4. Precipitate (c) still contained a considerable quantity of Mg, as evidenced by the NaOH and iodine test.

2. 48 mgrms. of Mg as sulphate were precipitated as MgNH4PO4. The precipitate appeared to be about four to five times larger than the precipitate (b) in the last experiment.

Quantitative Experiments with Mg and Al.

1. A solution containing 56 mgrms. of Al and 50 mgrms. 5 grms. of solid NH4C1 of Mg was diluted to 60 cc. alkaline (15 cc.). The mixture was boiled and filtered and were added, and then 2/N NH4OH until the solution was the precipitate washed thoroughly with hot water. Mg in the filtrate was estimated as MgNH,PO4. MgNH4PO4 found.. 0.2052 grm.

Mg originally present

=45 mgrms. of Mg

➡50 mgrms.

The

5 mgrms. of Mg therefore remain with the Al. 2. Al 56 mgrms., Mg 25 mgrms., NH4Cl 5 grms., NH4OH 15 cc.

In this case practically all the tion.

01136 grms. of MgNH4PO4 24.8 mgrms. of Mg.

25 mgrms.

Mg has remained in solu

In this case 33 mgrms. of Mg have been precipitated with the Al.

It is evident from these experiments that the greater part of the Mg may be precipitated along with the Al (probably as magnesium aluminate) unless a very much larger excess of NH4Cl is present than is usual in qualitative analysis. This would explain the frequent failure to detect Mg in an ordinary analysis.

The result is of course one which might be predicted from the fact that alkaline solutions favour the ionisation of aluminium hydroxide in the acid form. In all probability the solubility product constants of Mg(OH)2, Mg(AlO2)2, and Al(OH); decrease successively, in which case a concentration of OH' ion not sufficient to precipitate Mg alone as hydroxide might nevertheless in the presence of Al be sufficient to prevent the oncentration of the AlO2' ions falling below the value requ. by the solu bility product Mgx (AIO2')2. A further dec ase in the OH' ion conrent, following on the addition > more NH4Cl might then decrease the AlO2' ion concentration sufficiently to bring the product Mg× (AlO2)2 below the solubility coefficient value, and consequently Mg would remain in solution.

Fe and Ba.

1. A solution containing 112 mgrms. of Fe and 46 mrgms. of Ba as chlorides was treated with a few cc. of (NH4)2HPO4 solution and then with dilute HCl until the precipitated phosphates just dissolved. Some solid Na.C2H3O2 and 2 cc. of 2/N acetic acid were then added and the solution diluted to 40 cc. and boiled. Tle precipitate was filtered off and washed well.

The filtrate gave a small precipitate of BaSO4 on adding H2SO4.

The precipitate of FePO4 and basic ferric acetate was dissolved in dilute HCl and treated with a little H2SO4. A precipitate of BaSO4 was obtained roughly three to four times larger than that obtained from the filtrate.

2. Some FePO4 was prepared by precipitation and thoroughly washed with hot water until practically free from chlorides. A portion of this was boiled with BaCl2 solution for a few minutes, then filtered and washed with hot water until free from chlorides.

The filtrate gave a heavy precipitate of BaSO4 on adding H2SO4. The precipitate of FePO4 on dissolving in dilute HCl and adding H2SO4 gave a small precipitate of BaSO4, not more than about one-tenth of that obtained from the filtrate.

3. Another portion of the FePO4 was boiled up with a solution containing 46 mgrms. of Ba, I grm. of NaC2H3O2 and a few drops of 2/N acetic acid. The precipitate was then filtered off and washed free from chlorides, dissolved in dilute HCl and tested with H2SO4. A white precipitate of BaSO4 was obtained.

The filtrate was treated with H2SO4 and gave a precipitate of BaSO4, roughly equal in amount to that obtained from the FePO4.

4. 56 mgrms. Fe, 46 mgrms. Ba, 2 cc. 2/N (NH4)2HPO4, I cc. 4/N acetic acid, and 6 cc. 2/N Na.C2H3O2.

FeCl3 was added until the mixture was just yellow, after which the latter was boiled and the precipitate filtered off and washed. The filtrate gave a small precipitate of BaSO4. The precipitate of FePO4 and basic ferric acetate on dissolving in HCl and adding H2SO4 gave a very much larger smount of BaSO4.

Practically all the Ba remained with the FePO4. 5. To a solution containing 56 mgrms. of Fe, 46 mgrms. of Ba, 1 cc. 4/N acetic acid, and 6 cc. 2/N NaC2H3O2, 2 cc. of 2/N (NH4)2HPO4 were added in the cold. The precipitate was filtered off and washed carefully with cold water. On testing for Ba the precipitate was found to contain much more of this than the filtrate.

6. 56 mgrms. of Fe were precipitated as basic ferric acetate in presence of 70 mgrms. of Ba. The precipitate was filtered off and washed well. On testing it for Ba only a trace was found, while the filtrate was found to contain practically all the Ba.

7.56 mgrms. Fe, 115 mgrms. Ba, 7 cc. 05/N (NH4)2HPO4, I cc. 4/N acetic acid, and 8 cc. 2/N Na.C2H3O2. FeCl3 was added until the mixture was just yellow, and the latter was then boiled for five minutes and the precipitate filtered off and washed well. The filtrate and the precipitate contained about equal amounts of Ba. (To be continued).

Reports follow on the conditions under which the last harvests of 1914-15 took place, and very complete tables show the production of cereals of this year in almost all Northern Hemisphere countries.

Including several modifications from the Bulletin of November, the total crops of each cereal are as follow:Wheat. The crop for the following group of countries is officially estimated for 1915 at 989.740.769 quintals, against 826,607,938 in 1914, or 119.7 per cent of the latter amount:-Hungary, Bulgaria, Denmark, Spain, France, Great Britain and Ireland, Italy, Luxemburg, Norway, Netherlands, Roumania, Russia in Europe, Switzerland, Canada, United States, India, Japan, Russia in Asia, Egypt, and Tunis.

Rye. For the following group of countries the 1915 crop is officially estimated at 300,522,512 quintals, against 261,796.607 in 1914, or 114.8 per cent :-Hungary, Bul. garia, Denmark, Spain, France, Ireland, Italy, Luxemburg, Norway, Netherlands, Roumania, Russia in Europe, Switzerland, Canada, United States, and Russia in Asia.

Barley. The 1915 crop is officially estimated at 269,492,306 quintals, against 229,301,652 in 1914. or 117'5 per cent for the following group of countries :-Hungary, Bulgaria, Denmark, Spain, France, Great Britain and Ireland, Italy, Luxemburg, Norway, Netherlands, Roumania, Russia in Europe, Switzerland, Canada, United States, Japan, Russia in Asia, Egypt, and Tunis.

Oats.-The 1915 crop is officially estimated at 563,490,494 quintals, against 456,250.940 in 1914, or 123.5 per cent for the following group of countries :Hungary, Bulgaria, Denmark, Spain, France, Great Britain and Ireland, Italy, Luxemburg, Norway, Netherlands, Roumania, Russia in Europe, Switzerland, Canada, United States, Russia in Asia, and Tunis.

at

Maize. The 1915 crop is officially estimated 909,654,237 quintals, against 802.317,332 in 1914, or 1134 per cent for the following group of countries :Hungary, Italy, Roumania, Russia in Europe, Switzerland, Canada, United States, Japan, and Russia in Asia.

In the Bulletin there follow next reports on the rice, flax, cotton, potato, hop, tobacco, vine olive, and sugar beet and cane crops. More particularly is to be noted among the new data published on these crops the production of potatoes in Ireland, viz., 37,695.981 quintals, or 107.7 per cent of the 1914 crop, and in France (90.570,920 quintals, or 75'5 per cent), and also the wine production of Roumania, viz., 1.670.980 hectolitres, or 250'6 per cent of that in 1914, and of France, where the partial results referring to the four principal Departments of the South (Hèrault, Aude, Gard, and Eastern Pyrenees) give 9.556,840 hectolitres, or 32'4 per cent of the corresponding production in 1014.

The agricultural part of the Bulletin ends with data from the live-stock statistics of France collected at July 1, 1915, and at December 31, 1914.

The commercial part contains tables of imports and exports, stocks, and prices of cereals and cotton on the chief markets, the tables being as complete as possible under present conditions.