1000 2. That for every 1000 parts of sulphur used in the form of bisulphide of iron, the following oxygen must be admitted : 375 parts oxygen for the oxidation of the iron, 1000 formation of sulphurous acid, 500 conversion of sulphurous to sulphuric acid.
1875 As 1 litre of oxygen weighs 1.4298 grm. at 0° C. and 760 mm., the above weights will equal 375 grm. oxygen = litres, combined with 986.7 lit., nitrogen as air. 1000 ,, = 699.4 2631.1 ,500 , = , 1315.5 1875 , = 1311.4 4933.3 , Theoretically each 1000 grm. sulphur burnt out of the bisulphide of iron will require the admission of 1311.4 4933.3 = 6244.7 litres of air at 0° C. and 760 mm.
To this an excess of oxygen must be added, and manufacturers are agreed thst a greater excess is necessary with pyrites than with sulphur, and that it should amount to 6-4 parts by volume for each 93.6 parts nitrogen escaping from the chambers, or 6.4 per cent. by volume of the mixed gutes in a dry state. Let equal the unknown percentage of excess oxygen which must be 79 admitted, and the volume of nitrogen from which it must be liberated is x litres. The amount , of these two gases joined to the 4933.3 litres nitrogen introduced with the oxygen required for the formation of the sulphuric acid from the sulphur will give a volume of 79 100 4933.3 + x = 4933.3 64 100 But x = - of this volume, therefore we have x = (4933.3 + = (x = 4:54.4 100 100 Besides the theoretical 6244.7 litres of air necessary for every 1000 grms. or 1 kilo. of sulphur burnt from pyrites, there are then 454.1 litres of excess oxygen necessary, which is combined 454.1 ; 79 with = 1708.4 litres nitrogen ; that is, 2162.5 litres of air or a total of 8407.2 litres 21 of air at 0° C. and 760 mm. We have already seen that each 1 kilo. of native sulphur requires 6199 litres of air at 0° C. and 760 mm.; therefore, when the sulphur is derived from bisulphide 8407.2 of iron it needs = 1.356 times as much air.
6199 This proportion does not remain constant in the amount of gases admitted to the chambers. In burning pyrites, a part of the oxygen remains behind with the iron, while burning brim stone the total volume of air finds its way to the chambers without any change of volume, because oxygen does not alter its volume by oombination with sulphur to form sulphurous acid. The 8407.2 litres of air admitted to the kilns for each 100 grm. of sulphur from bisulphide will pro
duce an amount of gas passing into the chambers, as follows: 699.4 litres sulphurous acid, having the same volume as oxygen.
349.7 oxygen, for conversion of sulphurous to sulphuric acid.
454.1 in excess.
4933.3 nitrogen, theoretically attached to the oxygen as air.
1708.4 I/ /0 excess oxygen Total 8144.9 litres, of which 699.4 aro sulphurous acid, 803.8 are oxygen, and 6641.7 are nitrogen ; or proportionally 1 volume of the gas consists of 0'0859 sulphurous acid.
0'0987 oxygen.
0.8154 nitrogen.
1.0000 In many works the sulphurous acid amounts to much lees than 8 59, and is even under 6 per oent. of the gas volume. It is evident that in that case the amount of sulphuric acid formed in a similar chamber space will be reduced unless at the expense of an increased consumption of nitre.
According to previously given scales, 1 litre of the above gas will weigh (at 0° C. and 760 mm.) 0.0859; 2.8731 ± 0.0987 ; 1.4298 ± 0.8151; 1.2562 = 1.4122 grm., while 1 litre of the gas which passes into the chambers from the combustion of native biimstone weighs 1.4547 grm. The gas derived from pyrites is therefore lighter, and consequently creates a stronger draught than that from native sulphur.
As the amount of gas conveyed to the chambers for each 1000 grm. of sulphur as iron pyrites is 8144.9 litres, while that from 1000 grm. of native sulphur is only 6199 litres, then a certain weight of sulphur in pyrites produces 86141949.9 = 1.314 times as much gae as the same weight of sulphur in a free state.
The knowledge of this proportion is sufficient to enable the conduct of the process to be regulated in the same manner as we have already described for sulphur.
The Steam.-What has already been said regarding the admission of steam in the manufacture from native sulphur holds good also in this case. Thc supply, however, will vary because the volume of gas produced from pyrites is 1.314 times as great as that formed by brimstone, and because under constant conditions of temperature and pressure, the amount of steam that can be contained in the gases is in direct proportion to their volume. Consequently 1.314 times as much steam may be used with pyrites. As we have seen that 30.5 per cent. of the necessary water can exist as steam in the gases, that amount will be increased with pyrites to 30.5 ; 1.314 = 40.08 per cent.