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An Improved Hydrogen Sulphide Generator.
[Read before the Philosophical Institute of Canterbury, 2nd December, 1925; received by Editor, 31st December, 1925; issued separately, 8th March, 1927.]
An automatic hydrogen sulphide generator for laboratory installation has been described by Steele and Denham (Trans. Chemical Society, 1920, vol. 117, p. 527). Since then the present authors have redesigned certain portions of the apparatus, and the modified generator has given such highly satisfactory results during constant use for the last two years, that a description of it has been considered justified. A chemical laboratory fitted with one of these generators would have a potential and practically unlimited supply of hydrogen sulphide always at hand at the negligible cost of the electric current needed to keep the generator heated.
The following is a description of the apparatus:—
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A is the acid holder of about six litres capacity; B a tap funnel for use in filling A; C a two way tap so that A can be connected either to the tube D which leads to an outside flue, or to E to which is attached a length of rubber tubing (not shown); F is a large bore tap, situated at a higher level than the acid in A, by the turning off of which the flow of acid in the siphon G can be stopped; H is a reservoir of 600 to 700 c.c. capacity for retaining hydrogen sulphide generated but not withdrawn from the apparatus; J is a bulb of about 150 c.c. capacity, situated a few centimetres above the highest level of acid in A; K is 100 c.c. bulb; L is a piece of capillary tubing of 2 m.m. bore and of about 8 cm. total length, used to prevent a too rapid flow of acid when the taps are turned on, connected to the reservoir H by a piece of pressure tubing, I, which should be wired on; M is a small 10 c.c. bulb, N, P taps, R thick-walled rubber tubing, inserted for flexibility so that the rubber stopper S can be easily removed for recharging with sulphide; T is a wash-bottle, containing water, through which the hydrogen sulphide is supplied to the distributing taps and mains; V is a tube of fused silica, the upper portion of which is about 50 cm. long and 5 cm. internal diameter whilst the lower part is of 2 cm. internal diameter and fitted by a tight rubber stopper into the reservoir W, of six litres capacity which receives the spent acid; Y is a tap, through which the spent acid is withdrawn and which may conveniently be connected by a tube to a waste drain. The tube V is heated electrically.
In the authors' generator, the winding is made over a thin piece of asbestos paper with nichrome wire of one ohm per foot resistance, giving a total resistance of 100 ohms, and is well covered with many thicknesses of asbestos paper. This winding is connected through an ammeter and adjustable resistance to a 100 volt storage battery in such a way that by throwing over a switch the circuit either can be connected with the full battery of 110 volts or a portion of it, giving 60 volts. A current of just over 1 ampere is sufficient to heat the tube V up to working temperature in from 10 to 15 minutes while a current, of .6 ampere will maintain it at a temperature suitable for operation of the generator. The rate of consumption of electrical energy for steady working of the generator is thus only about 36 watts, a neglegible quantity.
Mode of Operation.—The tube V is packed with lumps of iron sulphide. The acid holder is filled by means of the funnel B with commercial hydrochloric acid diluted with an equal volume of water, and the funnel tap turned off. The taps F and N are turned on and the tap C turned so as to connect the acid holder to E, through which air is blown (through means of a rubber tube connection) until the siphon G fills. Tap N is then turned off and tap E turned so as to connect the acid holder with the tube D. The reservoir H fills to the side tube level with acid, which then runs over into V and, provided the current has been switched on sufficiently long to heat V, hydrogen sulphide is generated as soon as a few drops run over and drives the acid back into H, where the hydrogen sulphide is stored till drawn off through the tap P and washbottle T. The acid is completely neutralized long before it has percolated through the heated column of sulphide.
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The side tube Z and bulbs J and K are provided as an escape for hydrogen sulphide should an excessive amount be generated owing to some abnormal cause such as the turning on of tap F (when starting up) before the tube V is sufficiently heated. This prevents hydrogen sulphide from getting into the siphon and putting the generator out of action. When the generator is not in operation and the tube V not heated, tap F is kept turned off.
General Remarks.—The capacity of this generator is practically the same as of the one formerly described, while for economy in acid and sulphide consumption it is even better, practically theoretical yields of hydrogen sulphide being always available at a steady and convenient pressure. It has the following advantages over the older form.
(1) It is completely automatic in operation, needing no attention beyond turning on in the morning and off at night, and, of course, recharging with acid and sulphide at regular intervals (in the authors' case, once a week). From this point of view, electrical heating is a great advantage over steam heating, whilst the use of silica instead of glass for the tube V overcomes the trouble formerly experienced of cracking, due to alternate heating and cooling.
(2) There is complete absence of any acid leaks as acid never comes in contact with rubber stoppers or connections (except at I during a portion of the cycle of operations). The tap F is placed above the level of acid in A so as to completely eliminate any tendency of acid to leak around it.
(3) Provided the tube D is carried to a suitable flue, there is no smell of hydrogen sulphide about the generator which may, therefore, be installed unenclosed in a suitable position in the laboratory.
The hydrogen sulphide is distributed throughout this building in composition (lead) gas pipes of ¼ inch internal diameter without any serious loss of pressure. After three years, the attack on these pipes appears hardly to have penetrated beyond the inner surface, although in the experience of one of the authors at Brisbane, of subtropical climate, these pipes were seriously attacked, but this could probably be overcome by the use of drawn copper tube.