A SUPPOSED AMMONIUM SYNGENITE’ J. M. Ul%LI, AND W. C. TABER
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In a recent publication J. L)’Ans2 has shown that the double sulphate of ammonium and calcium, which he calls ammonium syngenite, exists at 2 5 O and even at lower temperatures. In our former paper3 in which we described a double sulphate obtained a t 50°, we stated that as Droeze, Cohn and Sullivan had not noticed a double sulphate, it was probable that it was not stable at 2 5 O , the temperature a t which Sullivan worked. There was, however, no record that they investigated solutions approachirig saturation with respect to ammonium sulphate, and consequently the possibility of a double sulphate at higher concentrations was not excluded. To the double sulphate of ammonium and calcium D’Ans has given the formula (NH,),SO,.CaSO,.H,O, based on its similarity in crystal form to syngenite, and on a determination of the composition of the solid product obtained by washing the double compound free of the mother-liquor by an alcohol-water mixture and then by an alcohol-ether mixture. This treatment is claimed t o cause no precipitation from the mother-liquor and also to cause but very slow decomposition of the crystals. I n order to determine the effect of this treatnient upon the solid residue, we have washed about 2 0 grams of the residue with about 75 cc of 50 percent alcohol in small portions, followed by washing with about 30 cc of a 50 percent alcohol-ether mixture in three portions, each time removing the wash liquid as far as possible by suction. The residue was then dried at about 40° until no,odor of alcohol or ether Published by permission of the Secretary of Agriculture. Berichte, 39, 3326 (1906). Jour. Phys. Chem., IO, 119 (1906). In this paper we misquoted the for the double formula given by Fritsche (Jour, prakt. Chem., 72, 291 (1857))~ sulphate of calcium and sodium, which should have been 2Na2SO,.CaS0,.2H,O and not Na2SO4.CaSO4.2H,O.
could be detected, requiring about ten minutes. In the following table are given the results of the analysis of this residue, and also the results of D'Ans. __
. ~ _ _ _ _ ~~
I
1 _~
~~
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D' Ans . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Authors ............................ Calc. from (NH,),SO,.CaSO,.H,O.. Calc. froni (NH4),S0,.CaS0,.2H,0..
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,
1 .I
_ ~ ~ ~ _ _ _ _
--
~~
Loss o n ignition
~
weig,led SOs weighed as CaO. asBaSO, ~
-~~
52 38 49.65 52.45 55.3
~~
I
1
14.28 15.21 14.00 13.17
-
1
53.46 55 91 52.60
From our results upon the loss on ignition after washing with various mixtures, it is evident that this treatment caused an increase in the quantity of lime in the residue. In other words, even if the formula proposed by D'Ans were correct, the above experiments prove that washing with an alcoholwater mixture deconiposes the compound rapidly, and consequently the results of D'Ans with a product so obtained are open to serious doubt. The concordance between the calculated and his observed value of the loss on ignition is probably due t o a smaller degree of decomposition than we have observed. A s the molecular weight of ammonium sulphate and calcium sulphate are very close, no conclusions can be drawn from the sulphate detcrmiiiations. Sonie water may also have been removed by the alcohol-ether treatment. It is apparent, therefore, that washing with a solvent to remove the mother-liquor, results in the decomposition of the crystals by the removal of ammonium sulphate and possibly of some water. To determine the composition of the crystals, an indirect method must be resorted to. We have repeated two determinations by the indirect method of residues, and both sets of figures confirm the formula which we gave in our former paper. These mixtures have stood a t room temperature (20') for about four months. By plotting these on a triangular dingrani and joining the corresponding points, both lines cross the line representing equi-molecular quantities of the sulphates, at the point representing 11.5 percent of water. From the formula which
494
J. M. Bell and W; C. Taber
~ _ _ _
~
~~
Solution
(NH,),so, Percent
Cas04 Percent
37 82 38.90
0.261 0.226
~~
- __ Residue
(NH,),so, Percent
, 1
42.15 42.49
i
I
CaSO, Percent
33.36 32.65
