EXCHANGE 8o6i "A"N Ammonium Phospho-molybdate THESIS PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF PENNSYLVANIA IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY BY V CHARLES MCDOWELL GILLAN, B.S. PHILADELPHIA, PA. 1909 PHILADELPHIA THE JOHN C. WINSTON CO 1 910 Ammonium Phospho-molybdate THESIS PRESENTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF PENNSYLVANIA IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY BY CHARLES MCDOWELL GILLAN, B.S. \\ PHILADELPHIA, PA. 1909 '' !% PHILADELPHIA THE JOHN C. WINSTON CO. IQIO x 4 ACKNOWLEDGMENT The author desires to express his gratitude to DR, EDGAR F. SMITH, for his advice and encouragement in this work, which was undertaken at his suggestion. AMMONIUM PHOSPHO-MOLYBDATE. INTRODUCTION. This salt has received considerable attention from analysts. The results of the investigations upon it have not been altogether satisfactory. There seems to be quite a wide difference in the ratios existing between the phosphoric acid and the molybdic acid. Indeed these range from 5 : 1 upward as high as 24: I. In no instance has the cause of this remarkable difference been definitely determined. In the opinion of Wolcott Gibbs 1 the formula for ammonium phospho-molybdate is, 24 Mo0 3 . P,0 5 . 3 (NH 4 ) 2 + XH 2 O. How r ever, in the course of his investigation there was dis- covered quite a large series of salts; these he classified as follows : 10 MoO 3 . 2 P 2 O 5 . 5(NH 4 ) 2 O. X H 2 OXr=(; or 20). 10 MoO 3 . 2 P 2 O 5 . 6(NH 4 ) 2 Q. 14 H 2 O 32 MoOa. 2 P 2 O 5 . 6(NH 4 ) 2 O. 28 H 2 O 44 MoOa 2 P 2 Q 5 . 6(NH 4 ) 2 O. 18 H 2 O 48 MoO 3 . 2 P 2 Q 5 . 5(NH 4 ) 2 O. 16 H 2 O 22 MoOa. i P 2 O 5 . 3(NH 4 ) 2 O. 9 H=O 22 MoOs. i P 2 O 5 . 3(NH 4 ) 2 O. 12 H S O 60 MoO 3 3 P 2 O 5 . 8(NH 4 ) 2 O. 12 H 2 O 16 MoO*. i P S O 5 . 3(NH 4 ) 2 O. 14 H 2 O 'In this study he was disposed to assign the following general formula to ammonium phospho-molybdate: m MoO 3 . 2P 2 O 5 . n R 2 O. X H 2 O. in which m is always an even number, varying from 10 to 48, while n varies from 3 to 6; it is usually 6, although it a Proc. Am. Acad. Arts and Science, 17, 62. (3) 444336 may exceed that number. R is ammonium, and generally equals 6. Wolcott Gibbs regarded those salts as normal in which there were six ammonium molecules, the salt having a ratio of 60 : 3 or practically 20 : I he regarded as acci- dental, and at the time, felt that further proof was necessary to establish its existence. This proof Debray 2 supplied later upon analyzing a salt which gave values corresponding to the formula, 20 MoO 3 . P 2 O 5 . 3(NH 4 ),O + 3 H 2 O. That the ratio 20:1 was correct, Debray felt was proved by the formula of the following silver salt : 20 MoO 3 . P 2 O 5 . 7 AgsO + 24 H 2 O. Debray, furthermore, described an ammonium salt in which the ratio of molybdic and phosphoric acid was 5:1. His analysis of this salt gave the formula, 5 Mos. P 2 5 . 3(NH 4 ),0 + 7 H 2 O. In addition he obtained the following derivatives : 5 MoOs. P 2 5 . 3 K 2 + 7 H 2 O. 5 MoOs. P 2 O 5 . 3 Na*O + 14 H 2 O. 5 MoOs. P 2 O 5 . 3 Ag O + 7 H 2 O. He maintained that salts of the higher series were decomposed by alkalies and passed into salts where the ratio of the acids was 5:1; conversely, that the addition of a mineral acid to an alkaline solution of the 5 : i salt, caused it to change to a salt of a higher series. Debray's study on ammonium molybdate in which the ratio of acids was 5 : I was, in reality, a confirmation of the work of Zenker, 3 who had previously prepared the salt: 5 MoOs. P O B . 3(NH 4 ) 2 O+7 H 2 O. 2 Bull. de la Soc. Chim. de Paris [2], 5^ 404. 3 Fresenius' Zeit. fur anal. Chem., 14, 12. Indeed, Rammelsberg 4 had also made this 5 : I salt. These results are highly interesting because they show the number of molecules of molybdic acid to be uneven, and the basicity of the complex acid seems to be 3 and not 6. To the neutral salt Rammelsberg assigned this formula: 22 MoOa. P 2 (X 3(NH 4 )tO. 12 H 8 0. At a later date, Wolcott Gibbs 5 repeated the work of Debray and was able to confirm the results obtained by the latter. Finkener, 6 from his studies, concluded that while the percentage of water and ammonia could vary within wide limits, the ratio between the molybdic and phosphoric acids was always 24: i. EXPERIMENTAL. In the preparation of the salts later analyzed by me, pure ammonium molybdate was dissolved in redistilled am- monia, and to this solution, after expelling the excess of ammonia, the sodium phosphate, dissolved in a definite vol- ume of water, was added. The mixture of the two solu- tions- was then boiled for one-half hour and acidulated with dilute nitric acid (1:3). The precipitates obtained after this fashion were uniform in color, with the exception of the salts number 6, 10 and n. All salts analyzed were dried to constant weight at a temperature varying between no and 120. In the analysis of the various compounds prepared by me, I had recourse to the methods which were suggested and used by Wolcott Gibbs in his study of the derivatives *Ber., 10, 1776. 5 Proc. Am. Acad. Arts and Science, 18, 232. c Ber., 10, 1638. of the complex inorganic acids. As these methods are familiar to analysts, mere reference to them will suffice. The details of their manipulation will be found amply given in the original papers of Gibbs. My aim was to ascertain, with a knowledge of the pre- ceding conflicting data, in regard to the constitution of com- mon phospho-molybdate, just what would result upon the use of the three sodium salts of phosphoric acid with definite amounts of molybdic acid, applied in the form of ammonium molybdate, under definite degrees of dilution. Accordingly, SALT No. i was prepared by bringing together 12 grams of monosodium phosphate and 14.4 grams of molybdic acid. This mixture was then boiled for one-half hour and acidulated with dilute nitric acid (1:3). There separated the usual yellow colored precipitate, which upon analysis, gave these results: .2068 grams lost .0191 grams upon ignition = 9.23% .2117 grams lost .0196 grams upon ignition = 9.28% .1923 grams lost .0176 grams upon ignition = 9. 17% .2091 grams lost .0193 grams upon ignition = 9. Mean = 9.22% .2296 grams gave .2082 grams mixed oxides = 90.68% .2016 grams gave .1829 grams mixed oxides = 90.72% .2196 grams gave .1990 grams mixed oxides = 90.62% .1914 grams gave .1644 grams mixed oxides = 96.63% Mean = 90.66% .;C2i6 grams gave .0132 grams Mg 2 P 2 O7 = 379% P 2 O 5 .2148 grams gave .0129 grams Mg 2 P 2 O T = 3.82% P 2 O 5 .2063 grams gave .0123 grams Mg 2 P 2 O 7 = 3.83% P2O 5 .1921 grams gave .0112 grams Mg 2 P 2 O T = 3.70% P 2 O 5 Mean = 3.78% P 2 O 5 .20i6 grams contained .0078 grams (NHOaO = 3.87% .2114 grams contained .0079 grams (NH 4 ) 2 O = 3.74% .1876 grams contained .0073 grams (NH 4 ) 2 O = 3.69% .1812 grams contained .0069 grams (NH 4 ) 2 O = 3.81% Mean = 3.74% MoO 3 by difference 86.88% P 2 5 378% (NH 4 ) 2 374% H 2 O by difference 5.48% Total 99-88% These results would lead to the formula: 22 MoO 3 . P 2 O 5 . 3(NH 4 ) 2 O. ii H 2 O. SALT No. 2. In this instance, di-sodium phosphate was substituted for monosodium phosphate. The quantities of material reacting were 14.2 grams of di-sodium phosphate and 14.4 grams of molybdic acid in the form of ammonium molybdate. This solution was treated as in the previous case, and when tne resulting yellow colored precipitate was analyzed, it gave the following results : .2019 grams lost .0186 grams upon ignition = 9.21% .2272 grams lost .0208 grams upon ignition = 9.16% .2116 grams lost .0198 grams upon ignition = 9.36% .1846 grams lost .0170 grams upon ignition = 9.21% Mean = 9.23% .2210 grams gave .2021 grams of mixed oxides = 91. 45% .1863 grams gave .1701 grams of mixed oxides = 91.30% .1921 grams gave .1754 grams of mixed oxides = 91.31% .2049 grams gave .1869 grams of mixed oxides = 91.22% Mean = 91. 32% 8 .2060 grams contained .0075 grams (NH 4 ) 2 O = 3.64% .2256 grams contained .0084 grams (NH 4 ) 2 O = 3. Mean = 3.68% .2145 grams gave .0127 grams Mg2-P 2 O7 = 3.78% P 2 O 5 1939 grams gave .0116 grams Mg 2 P 2 O-, = 3.82% P 2 O S Mean = 3.80% MoO 3 by difference ........................ 87.50% P 2 O 5 ...................................... 7.80% (NH 4 ) 2 .................................. 3.68% H 2 O by difference ......................... 5-55% Total .................................. 100.53% These led to the formula, 22 MoO 3 . P 2 O 5 . 3(NH 4 ) 2 O. ii H 2 O. SALT No. 3. Here 14.6 grams of tri-sodium phosphate were boiled up with 14.4 grams of molybdic acid. The resulting phos- pho-salt analyzed as follows : .2046 grams lost .0187 grams upon ignition = 9. 14% .2023 grams lost .0188 grams upon ignition = 9.28% .2097 grams lost .0194 grams upon ignition = 9.25% .2084 grams lost .0191 grams upon ignition = 9.16% Mean = 9.21% .2039 grams gave .1850 grams mixed oxide = 90.73% .2141 grams gave .1944 grams mixed oxide = 90.85% .2026 grams gave .1837 grams mixed oxide = 90.68% .2072 grams gave .1881 grams mixed oxide = 90.78% Mean = 90.76% .2043 grams gave .0113 grams Mg 2 P 2 O7 = . .2017 grams gave .0115 grams Mg 2 P 2 Oi = 3.62% Mean = 3.57% .2ogi grams gave .0068 grams (NH 4 ) 2 O = 3-25% .2109 grams gave .0071 grams (NH 4 ) 2 O = 3.37% .2014 grams gave .0065 grams (NH 4 ) 20 = 3.23% .2067 grams gave .0069 grams (NH 4 ) 2 O = 3.34% Mean = 3.29% MoO 3 by difference 7.19% P,0 5 3-57% (NH 4 ) 2 O 3-29% H,O by difference 5-92% Total .................................. 99-97% From these percentages, one may deduce the formula 24 MoO 8 . P 2 O 5 . 3(NH 4 ) 2 O. 13 H.O. SALT No. 4. The quantities of reacting substances were again changed as follows: 24 grams of monosodium phosphate and 28.8 grams of molybdic acid were brought together and treated as in the previous examples. The product of the reaction, when submitted to analysis, showed these results, .2072 grams lost .0195 grams upon ignition = 9.41% .2013 grams lost .0190 grams upon ignition = 9-44% .2057 grams lost .0192 grams upon ignition = 9.33% .2091 grams lost .0197 grams upon ignition = 9.42% Mean = 9.40% .2119 grams gave .1920 grams mixed oxides = 90.61% .2084 grams gave .1887 grams mixed oxides = 90.55% .2106 grams gave .1906 grams mixed oxides = 90.50% .2016 grams gave .1825 grams mixed oxides = 90.53% Mean = 90.55% .2039 grams gave .01 n grams Mg 2 P 2 O7 = 348 PaOs .2096 grams gave .0113 grams Mg 2 P 2 O7 = 348 P 2 O 5 .2054 grams gave .01 n grams Mg 2 P 2 OT = 346 P 2 0s Mean = 3.47 P 2 O 5 10 .21 16 grams gave .0078 grams (NH 4 ) 2 O = 3.69% .2047 grams gave .0073 grams (NH 4 ) 2 O = 3.56% .1991 grams gave .0071 grams (NH 4 ) 2 O = 3.57% Mean = 3.61% MoO 3 by difference 87.08% P 2 O 5 3-47% (NH 4 ) 2 3-61% H 2 O by difference 5-79% Total 99-95% From which there is deduced the formula, 24 MoO 3 . P 2 O 5 . 3(NH 4 ) 2 O. 13 HaO. SALT No. 5. Now substituting di-sodium phosphate and allowing 28.4 grams of it to react with 28.8 grams of molybdic acid, the product upon analysis showed: .2116 grams lost upon ignition .0230 grams = 10.87% .2043 grams lost upon ignition .0221 grams = 10.82% .2097 grams lost upon ignition .0226 grams = 10.78% .2106 grams lost upon ignition .0230 grams =10.92% Mean = 10.85% .2031 grams gave .1807 grams mixed oxides = 88.97% .1994 grams gave .1773 grams mixed oxides = 88.92% .2097 grams gave .1867 grams mixed oxides = 89.03% .2108 grams gave .1874 grams mixed oxides = 88.90% ,2041 grams gave .0133 grams Mg 2 P 2 Or = 4.i6% P^Os .2079 grams gave .0134 grams Mg 2 P 2 O7 = 4.i3% P 2 O 5 .2011 grams gave .0131 grams Mg 2 P 2 O7 = 4.i7% P 2 O 5 .2092 grams gave .0134 grams Mg 2 P 2 OT = 4.n% Mean = 4.14% P 2 O 5 II .2io6 grams gave .0083 grams (NH^O = 3.94% P 2 O 5 .2039 grams gave .0078 grams (NH 4 ) 2 O = 3.83% P 2 O .2016 grams gave .0079 grams (NHOaO = 3.92% P 2 O 5 .2009 grams gave .0076 grams (NH 4 ) 2 O = 3.78% P 2 O 5 Mean = 378% P 2 O 5 MoOs by difference 84.81% P 2 O5 4-14% (NH 4 ) 2 3.87% H,O by difference 6.98% Total .................................. 99-8o% Here the deduced formula would read, 24,Mo0 3 . P 2 5 . 3(NH 4 ) 2 0. 13 H,O. SALT No. 6. In its preparation 32.8 grams of tri-sodium phosphate and 28.8 grams of molybdic acid were boiled together. As tHe resulting yellow colored precipitate showed a rather high water content .upon analysis, portions of it were dried for ten hours at a temperature ranging from no to 120 C. This drying,' however, apparently made no change in the composition of the salt. Its analysis was as follows : .2063 grams lost .0422 grams upon ignition = 20.46% .2109 grams lost .0429 grams upon ignition = 20.34% 2097 grams lost .0426 grams upon ignition = 20.31% Mean = 20.3?-% .2061 grams gave .1635 grams mixed oxide = 79.33% .2039 grams gave .1621 grams mixed oxide = 79.49% .2106 grams gave .1670 grams mixed oxide = 79.29% .1982 grams gave .1573 grams mixed oxide = 79.36% Mean = 79-37% 12 .2043 grams gave .01 10 grams g 22 7 .2079 grams gave .0113 grams Mg 2 P 2 Ot = 3.46% P 2 O 5 .2013 grams gave .0106 grams Mg 2 P 2 O7 .2102 grams gave .0118 grams Mg 2 P 2 C>7 = 3. Mean = 346% P 2 O S .2016 grams gave .0073 grams (NH 4 ) 2 O = 3-62% .2097 grams gave .0073 grams (NH 4 ) 2 O .2056 grams gave .0071 grams (NH 4 ) 2 O = 3.. Mean = 3.52% MoOs by difference 75-91 % P 2 O 5 3.46% (NH<) 2 3-52% H.O by difference 16.84% Total 9973% The formula calculated from these percentages is, 22 MoO 3 . P 2 O S . 3(NH 4 ) 2 O. 39 H 2 O. SALT No. 7. On returning to monosodium phosphate, in this instance 24 g. of the latter dissolved in 300 c.c. of water were boiled with 28.8 grams of molybdic acid dissolved in ammonium hydroxide. The excess of the latter being expelled, the complex salt precipitated from this solution in nitric acid gave the following results upon analysis: .2116 grams lost .0433 grams upon ignition = 20.46% .2072 grams lost .0433 grams upon ignition = 20.27% 2057 grams lost .0419 grams upon ignition = 20.37% .2093 grams lost .0428 grams upon ignition = 20.45% Mean = 20.39% 13 .2O27 grams gave .1612 grams mixed oxides = 79.53% .2109 grams gave .1681 grams mixed oxides = 79.71% .2043 grams gave .1628 grams mixed oxides = 79.69% .2062 grams gave .1642 grams mixed oxides = 79.63% Mean = 79.64% .2019 grams gave .0114 grams Mg 2 P 2 O7 = .2042 grams gave .01 10 grams Mg 3 P 2 O T = 343% PzOs .2057 grams gave .0114 grams MgsPzOi = 3.52% P 2 O 8 .2022 grams gave .0112 grams Mg 2 P 2 O7 = 3.5i P 2 O 5 Mean = 3.52% P 2 O 5 .2116 grams gave .0075 grams (NH 4 ) 2 O = 3.54% .2076 grams gave .0072 grams (NH 4 ) 2 O = 3.47% .2091 grams gave .0076 grams (NH 4 ) 2 O=:3.64% .2078 grams gave .0074 grams (NH 4 ) 2 O = Mean = 3.55% MoO 3 by difference 76.12% P 2 O 5 3.52% (NH 4 ) 2 3-55% H 2 O by difference 16.84% These corresponded to the formula: 21 Mo0 3 . P 2 5 . 3(NH 4 ) 2 0. 37 H 2 O. SALT No. 8. This was obtained from 28.4 grams of di-sodium phos- phate and 28.8 grams of molybdic acid. Its analysis showed the following percentages : .2016 grams lost upon ignition .0413 grams = 20.49% .2054 grams lost upon ignition .0418 grams ==20.35% .2106 grams lost upon ignition .0432 grams = 20.51% .2029 grams lost upon ignition .0414 grams = 20.40% Mean = 20.44% .2063 grams gave .1641 grams of mixed oxides = 79.54% .2039 grams gave .1619 grams of mixed oxides = 79.34% .2002 grams gave .1592 grams of mixed oxides = 79.52% .2091 grams gave .1662 grams of mixed oxides = 79.48% Mean = 79.47% .2117 grams gave .0111 grams Mg 2 P 2 C>T = 3.35% P 2 O 5 .2042 grams gave .0108 grams Mg a P 2 O T = 3.38% P 2 O 8 .2091 grams gave .0113 grams Mg 2 P 2 Or == 3.44% PaOs .2076 grams gave .0114 grams MgaPaOt = 3.52% P 2 O 5 Mean = 3.47% .2129 grams gave .0080 grams (NH 4 )oO =3.76% .2147 grams gave .0084 grams (NH 4 ) 2 O = 3.9i% .2019 grams gave .0078 grams (NH 4 ) 2 O = 3.86% .2056 grams gave .0077 grams (NH 4 ) 20 = 3.74% Mean = 3.82% MoOs by difference 76.00% P 2 8 ,3.47% (NH 4 ) 2 3.82% H 2 O by difference * 16.62% Total 99.91 % The formula 22 MoO 3 . P 2 O 5 . 3(NH 4 ) 2 O. 38 H 2 O is readily deduced from the preceding percentages. SALT No. 9. This compound was made by the interaction of 32.8 grams of tri-sodium phosphate and 28.8 grams of molybdic acid. Its analysis showed, 15 .2071 grams lost .0405 grams upon ignition = 19.56% .2046 grams lost .0399 grams upon ignition = 19.50% .2057 grams lost .0398 grams upon ignition = 19.35% .2094 grams lost .0406 grams upon ignition = 19.39% Mean = 19.45% .2029 grams gave .1637 grams mixed oxides = 80.68% .2163 grams gave .1747 grams mixed oxides = 80.76% .2095 grams gave .1691 grams mixed oxides = 80.72% .2083 grams gave .1683 grams mixed oxides = 80.79% Mean = 80.74% .2116 grams gave .0118 grams MfePsOr = 3-55% P.Os .2149 grams gave .0119 grams Mg 2 P 2 Oi = 3.54% PzOs .2016 grams gave .0109 grams Mg 2 P 3 O T = 3-42% PaOs .2030 grams gave .01 n grams MgPO = 3.50% P 2 O 5 Mean = 3.50% P 2 O 5 .2052 grams gave .0079 grams (NH 4 ) 20 = 3.85% .2069 grams gave .0091 grams (NH 4 ) 2 O = 3-9i% .2007 grams gave .0079 grams (NH 4 ) 2 O = 3-94% .2151 grams gave .0082 grams (NH4) 2 O = MoO 3 by difference = 77-24% P 2 O 5 = 3-50% (NH 4 ) 2 O = 3-88% H,O by difference = 15-57% Total = 100.19% These values lead to the formula, 22 MoO 3 . P 2 O. 3(NH 4 ) 2 O. 36 H 2 O. SALT No. 10. Return was made again to the mono-sodium phosphate, 12 grams of which were boiled together with 14.4 grams of i6 molybdic acid. In the analysis of the product it was con- cluded to determine only the molybdic and phosphoric acid content. Analysis. .2072 grams gave .1655 grams mixed oxides = 79.87% .2098 grams gave .1674 grams mixed oxides = 79.79% .2032 grams gave .1624 grams mixed oxides = 79.92% .2051 grams gave .1636 grams mixed oxides = 79.77% Mean = 79.84% .2069 grams gave .0121 grams Mg 2 P 2 O7 = 3.72% P.O 5 .2046 grams gave .0118 grams Mg 2 P 2 C>7 = 3.67% P a O 8 .2017 grams gave .0115 grams Mg^Oi = 3.62% P 2 O 5 .2039 grams gave .0119 grams Mg-jPaOi = 3.73% P 2 O 5 Mean = 3.68% P,O 5 MoO 3 ....=76.16% ....= 3.68% Here the ratio of molybdic acid to phosphoric acid is as 20: i. SALT No. n. In its preparation, 12 grams of m'ono-sodiu.m phosphate and 21.6 grams of molybdic acid were used, that is, the latter was decidedly in excess. The salt which separated showed the following acid content upon analysis: .2055 grams gave .1528 grams mixed oxides =. 79.22% .2154 grams gave .1703 grams mixed oxides = 79.0670 .2022 grams gave .1599 grams mixed oxides = 79.08% .2235 grams gave .1772 grams mixed oxides =. 79.27% .1813 grams gave .0112 grams MgiFiOt =3.92% P 2 O 5 .2000 grams gave .0117 grams MgaPsOt = 3.75% PjOe .2029 grams gave .0126 grams MgtPaOr = 3,94% P O 3 .2913 grams gave .0182 grams Mg 2 P 2 O7 = 3.98% P O B Mean = 3.90% P 2 O 5 I? MoO 3 by difference ....................... = 75-28% P,O 5 ....................................... 3-90% Here the ratio of molybdic acid to phosphoric acid is 19:1. SALT No. 12. In this salt the quantity of mono-sodium phosphate con- tinued the same as in salts n and 10, while the molybdic acid content was increased to 36 grams. The product sub- mitted to analysis gave these percentages : .2835 grams gave .2204 grams mixed oxides = 77-74% .2211 grams gave .1721 grams mixed oxides = 77-84% .2088 grams gave .1624 grams mixed oxides = 77-77% .2439 grams gave .1899 grams mixed oxides = 77.86% .2664 grams gave .2071 grams mixed oxides = 77-74% Mean = 77-79% .2084 grams gave .0135 grams MgzPzOi = 3.91% .2058 grams gave .0123 grams Mg 2 P 2 O7 = 3-79% P=Os .2065 grams gave .0127 grams Mg a P 2 O7 = 3.92% P 2 O 5 .2217 grams gave .0142 grams Mg a PsOT = 3-88% P 2 O 5 Mean = 3.87% P 2 O 5 MoO 3 by difference = 73-92% P 2 O 5 , = 3-87% Hence the ratio of molybdic acid to phosphoric acid was again 19: i. SALT No. 13. The quantity of molybdic acid in this instance was 43 grams, while that of mono-sodium phosphate remained as before. Upon analysis of the product the ratio between the two acids was found to be 20: I. SALT No. 14. In this case 50 grams of molybdic acid was treated with 12 grams of mono-sodium phosphate. From the six analyses made to determine the-acid ratio the result was 19 : i of MoOs to P 2 O . i8 SALT No. 15. Continuing as before to increase the quantity of molybdic acid while continuing the preceding amount of mono-sodium phosphate the analysis of the product, which was repeated six times, showed the acid ratio in the salt to be 18 MoO 3 : i PsOn. SALT No. 16. In this instance the same idea of increasing the content of molybdic acid was preserved, so that 64.8 grams of this acid were boiled together with 10 grams of mono-sodium phosphate. The eight analyses made to determine the acid content proved that the ratio of these was 22 MoO 3 : i PsOs. SALT No. 17. Here 72 grams of molybdic acid and 12 grams of mono- sodium phosphate interacted. On analyzing the product the ratio of molybdic acid to phosphoric acid was found to be as 18: i. SALT No. 18. In making this salt the quantity of molybdic acid equaled 108 grams, with 12 grams of mono-sodium phos- phate. The analysis of the resulting product showed the acid ratio to be 19 MoO 3 : i P 2 O 5 . SALT No. 19. With 144 grams of molybdic acid and 12 grams of mono-sodium phosphate, the crystalline complex salt showed the acid ratio to be 19 MoO 2 : i P 2 O 6 . SALT No. 20. In this instance 24 grams of mono-sodium phosphate and 14.4 grams of molybdic acid were brought together in 150 c. c. of water. They were boiled for some time and upon the addition of nitric acid the usual yellow colored precipitate separated but in small amount. When it was analyzed it showed an acid ratio of i6MoO 3 :i P 2 O B . Other salts were prepared, with, however, the same varying results. If the experiences recorded in the pre- ceding paragraphs be tabulated, they would appear as follows : Salt used Mols. taken Mols. found Salt MoOa H 2 O MoOj P 2 8 (NH 4 ) 2 OH 2 NaH 2 PO 4 .1 mol. wt.. .1 mol. wt. 150 c. c. 22 3 II NaH 2 PO 4 .1 mol. wt. .15 mol. wt. 150 c. c. 19 NaHaPO* .1 mol. wt. .25 mol. wt 150 c.c. 19 NaH 2 PO 4 .1 mol. wt. .3 mol. wt. 150 c. c. 2O NaH 2 PO 4 .1 mol. wt .35 mol. wt. 150 c. c. 19 NaH 2 PO4 .1 mol. wt. .4 mol. wt. 150 c. c. 18 NaH 2 PO 4 .1 mol. wt. .45 mol. wt. 150 c. c. 22 NaH 2 PO 4 .1 mol. wt...5 mol. wt. 150 c.c. 18 NaH 2 PO 4 .1 mol. wt .75 mol. wt 150 c. c. 19 NaH 2 PO 4 .1 mol. wt. .1 mol. wt. 150 c. c. 19 NaH 2 PO 4 .2 mol. wt ,2 mol. wt. 150 c. c. 24 3 13 NaH 2 PO 4 .2 mol. wt. .2 mol. wt 300 c. c. 21 3 37 NaH 2 PO 4 .1 mol. wt .1 mol. wt 300 c. c. 2O Na 2 HPO 4 .1 mol. wt .1 mol. wt 150 c. c. 22 3 ii Na 2 HPO 4 .2 mol. wt .2 mol. wt. 150 c. c. 2O 3 13 NaaHPCX .2 mol. wt. .2 mol. wt. 300 c. c. 22 3 38 Na 3 PO 4 .1 mol. wt .1 mol. wt 150 c.c. 24 3 13 Na 3 PO 4 .2 mol. wt. .2 mol. wt. 150 c. c. 22 3 39 Na 3 PO 4 .2 mol. wt .2 mol. wt. 300 c. c. 22 3 36 An inspection of these results would show that six of the salts that have been analyzed show the ratio of acids to be 22 MoO : i PaO B ; 20 three show the ratio 20 MoOs : i PaO 8 ; five show the ratio of : 19 MoO 3 : i P 2 O 8 ; two show respectively the ratio of 18 MoO 3 : i P 2 O B , and 24 MoO 8 : i P 2 O B , while one salt gave the ratio 21 MoO 3 : i P 2 O 8 , with no apparent reason for the variation. Hundeschagen, 7 however, has proved that ammonium phospho-molybdate prepared in the usual way invariably carried with it two molecules of mineral acid; also that salts dried below 130 varied greatly in composition, and not until they were dried above that temperature was the composition likely to be constant. From his results he deduced the formula 12 MoO 3 . PO*. (NH 4 ) 2 O, thus giving an entirely new ratio. While the results of my investigation do not conclu- sively demonstrate the exact composition of ammonium phospho-molybdate, it is evident that they do contribute to the idea that the conditions of formation largely determine the constitution of the salt, and it is evident that to get a constant ratio for the acid content it is necessary to work under very definite conditions as to quantity of material present, and as to the dilution of the solution in which the complex salt is formed. 'Fresenius' Zeit. fur Analyt. Chem., 28, 141. UNIVERSITY OF CALIFORNIA LIBRARY