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For larger operations the “Jewel” gas-stove, Fig. 58, manufactured by Geo. M. Clark & Co., Chicago, will be found very serviceable. The cast-iron frame is twelve inches square and five inches high, thus standing very
Fig. 58. firm and capable of supporting large vessels. The gas is properly mixed with air before it enters the radial burner, where perfect combustion is effected, as shown by the pale-blue flame, which can be turned Jewel gas stove. down very low without flickering. It consumes about eight feet of gas per hour, and is a most efficient heater.
For regulating the degree of heat within certain narrow limits, special appliances have been devised, kuown as thermostats, by means
The Bunsen Kemp gas regulator or thermostat.
of which the supply of gas admitted to the burner is automatically controlled by expansion and contraction of mercury contained in glass cups or tubes kept in contact with the air or liquid the temperature of which it is desired to maintain at, or near, certain points. All gas supplied to the burner is made to pass through the thermostat, and the required temperature having been reached, the gauge is set by means of a screw, after which the supply of gas is controlled by the expansion of the mercury caused by an increase of heat. Figs. 59 and 60 show two thermostats frequently employed.
The steam boiler, Fig. 61, designed by Prof. E. L. Patch, is a
most convenient source of heat for the requirements of a small laboratory. The boiler, 22 inches high and 10 inches in diameter, is made of steel, contains 20 flues, and is covered with a thick layer of asbestos composition, to prevent loss of heat by radiation ; it has a capacity of 7 gallons and possesses one great advantage—that it can be heated by means of either a gas or a coal-oil stove. Being provided with a water-gauge, safety-valve and manometer, the boiler is as complete as any of larger size, and steam can be carried from it to any point desired; it is usually filled from above at the safety-valve, but, wherever water service is available, an injector may be attached, so as to allow of filling while steam pres
sure is ou. The coil of pipe in the conically shaped metal case on the side, may be used for hot filtration, evaporation or drying purposes.
It is well known that steam, when confined, is capable of absorbing large quantities of heat, and its temperature rises proportionally to the pressure exerted upon it; dense aqueous solutions, therefore, can readily be boiled by means of superbeated steam.
For the proper control and distribution of heat, different devices are employed. When direct flame is to be applied to porcelain or glass vessels the interposition of wire-gauze or asbestos cloth will be found very desirable ; for not only will the heat be supplied to a greater extent of surface by radiation, but at the same time it will
Sand-bath, shallow form.
Sand-bath, deep form.
be uniformly distributed, and thus insure more regular heating, which of itself is very important, considering the frail character of flasks and dishes.
The sand-bath is employed for temperatures above that of boiling water, and is chiefly intended to maintain a continuous supply of high
Large cand-bath, heated by steam.
heat and to prevent sudden depression of temperature from foreign causes; it is invaluable in the distillation of certain liquids (acids, etc.) from glass vessels, and may be either of deep or shallow form. (See
Figs. 62 and 63.) The deep sand-bath consists of an iron pot or basin containing sufficient dry fine sand so that, if desired, the retort or flask may be entirely surrounded by the same. The best shallow sand-baths are made of Russian sheet-iron, and are well adapted for heating flasks and beakers, which require only sufficient sand to form a good bed of support, since an excessive amount would involve a waste of heat.
For use in a laboratory where steam is available, a permanent sand-bath may be provided as shown in Fig. 64. It is constructed from an ordinary galvanized-iron sink and large gas-pipe, about three-quarters to one inch in diameter, arranged horizontally in folds, the ends of the pipe being introduced through holes of appropriate size drilled in the end of the vessel. Sand to the depth of two or three inches may be poured over the pipes, which will form an excellent bed for flasks, dishes, and beakers.
Other apparatus for the use of heat above that of boiling-water, yet avoiding contact with flame direct, are oil-baths, saline solution baths, glycerin baths, or paraffin baths; these are constructed like water-baths, and readily furnish temperatures ranging from 100° to 300° C. (212° to 641° F.).
For all operations requiring a degree of heat below that of boilingwater, water-baths will be found indispensable; they may be made with either a round or flat bottom, as shown in Figs. 65 and 66, and
provided with a set of concentric rings to adapt them for use with dishes or flasks of various sizes. Water-baths made of extra heavy tin will last a long time (provided they be dried properly after use), and do not cost much, while copper is far more expensive, but, on the other hand, resists the action of heat and water better than tinned iron. As long as the vapor of boiling water is allowed to escape freely, no amount of heat applied to the vessel can possibly increase the heat of the water above that of boiling, and, as some heat-power is lost during transmission from the water-bath to the vessel resting upon it, the liquid contained in such vessel will always be found a few degrees lower in heat than the water in the bath ; under no circumstances can aqueous liquids be made to boil in dishes placed in water-baths.
The name vapor-bath is in the majority of cases more appropriate than water-bath, since the vessel heated by it does not, as a rule, come in contact with the water for any length of time, but derives its heat from the vapor or steam rising from the water and not confined by pressure.
To avoid frequent refilling and consequent interruption in longcontinued operations, water-baths are often provided with a constant supply attachment as shown in Fig. 67, which also serves to keep
the water at a constant level in the bath. The best contrivance for a constant water-bath is that suggested by Dr. B. F. Davenport, of Boston, and shown in Fig. 68. It covsists of a copper box, A, 10 or 15 inches square, the top being a brass plate } inch thick, to enable it to bear considerable weight without yielding. From the point B projects a 1 inch brass tube, B C, which turns up at a right angle. At E is a stopcock which is connected by a thick rubber tube with the glass tube, D F, the latter being fastened against the adjoining wall. Connected with C by a rubber tube-joint is a 1 inch block tin tube of 20 feet length, which extends up the wall, to which it is fastened for 10 feet to the point T, whence it returns and ends just over the top of the glass tube at D. The bath is filled with water (preferably distilled) to just the level, B..b. The steam generated by the constant boiling is condensed in the tube, CT D, either before or after reaching the top, T, and returns to the bath at C or at D, where it drops into the glass water-gauge, DF. Having once been filled, the water need not be replenished for years, and there being no outlet for the steam, except into the condensing tube, the air surrounding the water-bath will be kept constantly dry-a very