The charge for each pitcher is from 18 to 20 lb. of the mixed acids, according to their strength, and when ready, all are set in place in the troughs, covered with glass plates and surrounded with ice and water, when they are allowed to stand until the acid in the pitchers has fallen to the temperature of the surrounding ice water, when the covers are removed and the air tubes passed through holes in the hoods down into them, then they receive a strong current of air from a pump driven by steam. The air current keeps the contents of the pitchers continually agitated, and is rendered perfectly dry by being drawn through sulphuric acid, whilst it is thoroughly cooled just before it enters the air main over the troughs. The glycerine in 2 lb. charges is then allowed to flow, and as each tube C C is a siphon, it is started by drawing through a glass tube in the outer end. As soon as the glycerine runs freely, the suction tube is withdrawn and a fine glass jet is substituted for it, from which a stream is directed into the pitcher be neath. Should the glycerine be too thick to flow easily, which occurs in cold weather, the bottles aro warmed as much as may be necessary by the steam pipe G. The glycerine, as it flows into the acid, is rapidly acted on and converted into nitro glycerine, the reaction taking place being represented by C, II, 0, + 3 II N 0, = Os N, 0„ + 3 and is accompanied by a consider able evolution of heat, which must be removed ; for should the temperature rise too high, the glycerine is oxydized and forms other substance. If the temperature is started at 0° (32° F.), it should not bo allowed to exoeed 9° (48° F.); and at 10°-I3° there is a great danger of firing taking place, hence the necessity for keeping the liquid in the pitchers cold, both by surrounding with ice-cold water and by means of the air current passing into the acid. The latter performs most important work, as by keeping the acid mixture in constant agita tion, the heat which is generated is quickly diffused through the whole, aud prevents any sudden local rise of temperature. The glycerine is much lighter than the acid, and is liable to collect in little pools above it, and if these were broken up and a quantity of glycerine suddenly brought into contact with the acid, the notion would ho so rapid that it could not be controlled. This, of course, cannot take place if the whole mixture is kept in constant agitation. Thertnometrical obser vations are frequently made while the glycerine is running into the pitchers, and if the temperature is found to be rising too rapidly, the glycerine is then running too feet, and its flow is checked by pressing down the short stopper e, which slightly compresses the rubber tube, so that less liquid can pass.
Should the temperature continue to rise the plug is forced tighter in, closing the glycerine tube altogether, when the flow is stopped and the contents of the pitcher cool rapidly. As soon as the proper degree is indicated the plug is loosened and the flow again set up. If the limit of tem perature is exceeded firing takes place, indicated by copious evolution of red nitrous fumes, and in extreme cases by flames. Usually when this action occurs it is easily controlled by stopping the stream of glycerine and stirring the mixture vigorously, but if it is violent the vessel must be at once emptied into water.
Acid and other irritating fumes are given off in large quantities during the operation of conver sion, and these are removed through the hoods into the chimney, which is in communication with a fire, or other suitable means for causing a powerful draught, which draws all the fumes upwards and enable them to he discharged into the open air; the arrangement indicated on the plan is of course unimportant, and can be conveniently modified if required. As soon as the requisite quantity of
glycerine has been run into the pitchers the conversion is complete, but the nitro-glycerine has to be separated from the large quantity of acid still remaining. This is almost entirely sulphuric, as the nitric acid has been nearly all used up in reaction. The nitro-glycerine is partly in solution and partly suspended in the heavy acid liquid. On diluting the acid the portion in solution is precipitated, and the whole of the nitro-glycerine settles to the bottom.
Fig., 622 is of the separating and washing apparatus. A large wooden tub A is sunk through the floor of the converting room ; it is filled about three-quarters with water, and has a cover with a square opening in which is placed a leaden strainer ; by means of a rubber hose connected with an air pipe a cur rent of air is led to the bottom of the tub, and vigorously agitates the water in it ; the pitchers, when taken from the con verting room, are emptied through the drainer into the tub, when the acid liquor descends in fine streams and is diffused through water.
When all the pitchers have been emptied the air pipe is withdrawn and a short time allowed for settling, the heavier nitro-glycerine collects at the bottom, so that the lighter acid water may be drawn off from above it, a wooden stop-cock b at the aide of the tub, a abort distance from the bottom, but above the level of the nitro-glycerine, serving to pass off the acid liquid by means of a short length of hose into the drain G; the nitro-glyceriue is drawn off in small quantities into the washing tub B through the wooden cock k, which is fitted in the lowest part of the inclined bottom of A.
The wooden tub B is lined with lead and supported by trunnions in a wooden frame c, the trunnions being placed just above the centre of gravity, so that the tub will stand upright and yet be easily turned or inverted ; pipes D and E are provided with valves within easy reach of the workmen standing by the tub ; one ie for water, and there is attached to it a short piece of hose, the other is connected to the air main, and has a length of hose sufficient to reach to the bottom of the washing tub.
The portion of the nitro-glyce• Me having been drawn into B, the air hose is put in and a stream of water turned on, the air current causes a strong ebullition, raising the nitro-glycerine and spreading it through the water ; as anon as the tub is full the latter is turned off, the hose removed, when in a few minutes the nitro-glycerine rapidly settles to the bottom, and the water may be poured off by turning the tub on its trunnions. This is repeated until the nitro-glycerine is thoroughly washed, when it is poured into a copper pail, from whence it is poured into earthen jars and allowed to stand covered with water until it clears ; it is then ready for use. The wash water decanted from B falls first into the tub C, from which the water runs off by the siphon pipe F into the drain g. Thus any nitro-glycerine which may have floated or been accidentally poured into C has an opportunity to settle, and so be saved. With any apparatus such as that described, employing 21 pitchers, about 80 lb. of nitro-glycerine can be made in 5 hours, not including the time required for cooling the pitchers, which will vary with the season of the year.