The accompanying sketch (Fig. 83) of a combined steam-oven and distilled water apparatus, so arranged as to be left to itself for a long period of time without the risk of the boiler going dry, may perhaps be of interest to many, and a few words only are necessary to describe its working. The steam oven a is of the ordinary construction, but is fitted at the side with a tube connecting it with the condenser b. Heat is applied to a by means of a radial burner, connected with the gas supply by metallic tubing; the steam generated circulates around the drying chamber, escapes through the copper tube c, thence through block-tin worm, and falls as distilled water in the receiver d. The cistern e, fitted with a Mariotte's tube holds cold water, which falls through the tube /, enters the condenser, where it rises slowly, absorbing heat from the condensing-worm, until it reaches the tube leading to the boiler at a high temperature. For a cistern, an 18-gal. ale cask, supported on a stool, has been found to answer admirably, having the advantage of holding sufficient water on the top to secure the 2 corks being airtight.
By a suitable adjustment of the Mariotte's tube A, the rate of flow of the water can be so regulated that the level of the water in the condenser is constant, or, if desired, allowed to drop slowly into the waste pipe, while the water evaporated from a is renewed by water already near boiling. In practice it has been found necessary to allow the water to waste at the rate of about 2 drops per minute, the 18 gal. lasting for over 72 hours, during which time 10-11 gal. of distilled water are collected. When this apparatus was first fitted up in the laboratory, it was intended to have connected the condenser directly with the town water supply, but as the water-works authorities would sanction no such connection, we had recourse to the cistern, with the satisfactory result that we are in this respect quite independent of the caprice of the water-works turncock. The several connections are made by union joints, to allow the apparatus to be taken to pieces and the boiler freed from scale. The whole apparatus may be supported upon a strong shelf, which should be protected from the heat of the burner by means of slates or asbestos millboard.
With this arrangement, bulky precipitates may be allowed to remain in the steam-oven all night and found ready for further treatment next morning. (Chemical Seas.).
Prof. Peter T. Austen, of the Chemical Laboratory of Rutgers' College (N. J.), says: We hare used for a number of years in this laboratory, a form of constant water-bath, Fig. 84, which was contrived by Edward Bogardus, formerly chemist to the New Jersey State Geological Survey. It consists of 2 tomato cans connected by a tin tube. Into one of the cans a bottle of water is inserted (e. g. a Mb. acid bottle), the other can makes the bath. This bath can be left Overnight without risk, and a number of baths can be similarly fed by connecting them by means of a rubber tube with a single reservoir, made of a fruit can with a number of holes punched near its bottom, perforated corks carrying short pieces of glass tubing being fitted to the holes. A similar contrivance can be used to make the connection with the can serving as the water-bath. Such vents in the by means of short bits of rubber tubing and pinch-cocks. Fig. 85 illustrates a water-bath constructed on the principle of Mariotte's flask. a serves as reservoir of water and is closed airtight by the perforated, rubber stopper b.
Through the latter pass 4 glass tubes, one of which, e, acts as a siphon, in connection with the rubber tube d, to supply water to the bath. The level in the latter is regulated by the depth to which the lower and of tube e reaches. The other 2 tubes, f and g, are closed while the apparatus is working, and are only used for filling it. When this is necessary, the pinch-cock at h is made to compress the rubber tube, the stopper i of the tube g is opened, and water is admitted to the flask through kI. If it is inconvenient or impracticable to keep the short rubber pipe I constantly connected with a water faucet, it may, when the flask is filled, be detached, and the open end pushed upon the glass tube g. In which case it is not necessary that the latter be provided with a stop-cock. By attaching several branches to tube d, any number of water-baths may be kept supplied at one and the same time. (Klement)
According to Pomeroy's plan, a tube of glass or metal, not less than 1/4 in. internal diameter, the ends of which are cut off obliquely (this is necessary), is bent as shown in Fig. 86. It should make an angle of about 30°, or a little greater, with the horizon, and the angle may be increased if the bore of the tube is increased. One end is inserted into the water-bath, the other into an inverted bottle. The height of the water in the bath is regulated by the depth of immersion of the tube in it. The boiling is not interrupted by the feeding, which takes place slowly and regularly. The same form of tube answers equally well for keeping a constant level of fluid in a filter or drying chamber. A brass tube is much better than one of glass, as it does not crack at the water level after use for a time. To bend brass tubes, ram them full of sand, stop the ends, and bend over a curved surface.
Seelig has communicated a method of preventing the loss of water, from evaporation, in drying ovens; and of confining the consumption of gas, at the same time, to the smallest possible quantity. The outer shell of the drying oven must have only one exit, communicating with the water space between the walls. Into this opening, the apparatus shown in Fig. 87 is firmly fastened by means of a perforated stopper surrounding the leg a. The lateral branch b communicates with the source of gas, and the branch c is connected with the burner under the drying oven. The tube a is expanded above, and closed by a rubber membrane d. This prevents, in the first place, loss of the water by evaporation. As soon as the tension of the steam in the apparatus has become higher than it was at the time of adjusting the apparatus, the membrane bulges upwards, closes the outlet of tube c, and thereby diminishes the supply of gas to the burner. The total extinction of the flame is pre vented by a scant supply of gas reaching the burner through a small lateral opening in the inner leg of c.
It will be readily seen that, if the apparatus is adjusted at the time when the water has actually reached the boiling-point, it may be kept for any length of time at the temperature of boiling water without having to renew the latter. (Zeit. An. Chem.)