360 ox TWO NEW CRYSTALLINE COMPOUNDS 



determined within five or ten minutes. In all these cases, however, the values of the 

 angles given above were included within the limits of uncertainty. 



DO * 



The faces of the crystals of SbZn^ are not generally so perfect as those of SbZus, nor 

 is their tabular fonn so well adapted for measurement. Moreover, variations in some 

 of the angles have been noticed in crystals from the same crystallization, amounting 

 even to ten minutes. The angle O on 1, however, appeared to be very constant, for in 

 all cases where it could be accurately measured the same value was obtained. As none 

 of the crystals of SbZn^, containing an excess of antimony, could be measured with 

 precision, no constant variation of angle could be detected, and, on the other hand, it 

 could not be proved to be invariable. 



Affiniti/ for Oxygen. 



The affinity of the crystals of SbZug of different compositions for oxygen was esti- 

 mated by boiling alloys of the same composition as the crystals with water, and meas- 

 uring the amount of hydrogen evolved in a given time. The following table contains 

 the results of these experiments. Column 1 gives the number of cubic centimetres 

 of hydrogen obtained by boiling 200 grammes of different alloys (granulated) with 

 water. The per cent of zinc contained in the alloys is given at the left-hand side 

 of the table, opposite to the number of cubic centimetres. The composition is known 

 only synthetically. The alloys were made by melting together the zinc and antimony 

 of commerce in the required proportions, making no allowance for impurities, and 

 when melted, they were granulated as nearly as possible under the same conditions. 

 Two hundred grammes of each alloy were boiled with water, the gas collected over 

 water, and the number of cubic centimetres evolved in an observed time read off after 

 the gas had been cooled to 20° C. These amounts were afterwards reduced for ten 

 minutes, and, thus reduced, are given in the table. As it was impossible to obtain 

 granules of a uniform size in all the alloys, another set of experiments was made in 

 a precisely similar way, except that the alloys were cast into small cylinders of a uni- 

 form size. As these cylinders had absolutely the same diameter, and very nearly the 

 same specific gra^-ity, throughout, the same amount of surface was obtained by weigh- 

 ing out 200 grammes of each alloy, and taking care to have the same number of little 

 cylinders in each lot. Column 3 gives the results of these experiments. It will be seen 

 that the two sets of numbers compare as closely as could be expected, it being remem- 

 bered that the amount of surface in the first set of experiments was variable, while that 

 in the second was constant, and smaller than the first. These results, however, are only 

 approximate. The limits of variation in different experiments on the same alloy would 



