permits the use of only very small relay currents with most other regulators. Since the contact is always made in an atmosphere of hydrogen, the amount of current which may be used in this regulator is limited only by the volatilization of the mercuiy a t the contact point. If too large currents are used, the mercury will spatter an-ay and so cause the bath temperature to vary. Currents u p to 0.5 ampere may be used if a small coiideiiser is placed in parallel with the contact. Hoir ever, better regulation is obtained with small currents. I n operation this regulator is entirely closed. Hence there is no danger of mercury vapors no matter what the temperature of the heated bulb may be, provided the pressure does not becomr too great for the instrument. Therefore this type of regulator has been used to control furnaces a t temperatures even above the boiling point of i-nercury (3). This is accomplished by making the vertical distance from the heated bulb to the stopcock E about 30 cin. or more. The pressure of this coIuniii of mercury prevents the boiling of the mercury a t temperatures well above its normal boiling point. If the heated bulb is horizontal, the mercury in the tube below E is not heated by convection. This is important in order that the grease in the stopcock may not be melted. Better regulation is obtained if capillary tubing is used. The useful range of the mercury thermoregulator is thus extended from the freezing point to above the boiling point of mercury. Lowtemperature furnaces may be easily regulated without resort to expensive equipment. Less-Sensitive Thermoregulator I n many cases i t is not necessary to control a constanttemperature bath to 0.001" or 0.01' C. There are bimetallic
regulators on the market, for use in a thermostat, which will respond to a change of approximately 1.0" C. The regulator shown in Figure 2 is intermediate in sensitivity between the very sensitive mercury regulator and relay and the bimetallic regulator. I t operates differently from the other in that the expansion of the regulator liquid directly opens the heating circuit. It will make and break a current of 0.5 ampere a t 110 volts without trouble. It has been used with currents a i high as 1.5 ampere a t 110 volts. If more than 55 watts energy is required to heat the bath, it is supplied by other heaters so designed that they mill not keep the bath a t quite the desired temperature. The final heating is accomplished by a 50-watt heater in series with this regulator. I t s sensitivity is *0.5' C. over a period of several hours. Changes in barometric pressure will have some effect on the temperature of the thermostat. The entire regulator is made of Pyrex and the electrical lead wires are of tungsten. Varying amounts of hydrogen were tried in the contact chamber. A comparatively small amount, as indicated in the illustration, was most effective. This regulator is filled with hydrogen in the same way as the one first described, but in the sealing-off process the tube Iheusual way. A piece of thin copper sheet with a hole in it is extended from the clamp jaw u p and over the end of the larger glass tubing. Operation
Vlien the safety device is operating. the single thron- switch muat be closed. As long as the Falinestock rides high enough
SO that it does not touch the copper strip, 110 current flon-s through the flexible cord or the single-thron- $witch hut may flow through the three-heat svitch axid thus heat u p the water which is kept a t a constant level. If the h t t l e of distilletl water is allowed to become dry for any reason. the float will xiiik with the level pf the water until the Falinestock toiichw the copper strip. niaking a direct short-circuit across the 20ampere i w e . nliicli burn.; out immediately. thus cutting C J ~ Y the source of heat to the heating element.
A Rapid Bulk-Sample Drier' T. H . Hopper SOnTH
I
D I K O T .. ~ ~ < ; n l c L ' L T l ' K . \ I . COI.LECE F.m(;o, K . D
S THE preparation of iiiaterials of plant or aiiiiiial origin
for chemical analysis it is frequently necessary to dry bulk samples to an air-dry condition. In such cases it is desirable and frequently necessary, in addition to rapid dryiiig, to dry the material a t a reduced temperatiup.
Figure 1-Drier
for Bulk S a m p l e s
The writer has found the apparatus shown in Figure$ 1 airti 2 both useful and successful for this purpose. I t consists cssenbially of three part's: (1) motor driven volume blower having a capacity of about 300 cubic feet, (8.5 cubic meters) of air per minute; ( 2 ) a baffle box 18 inches (46 cm.) wide. 36 inches (91 em.) long, aiid 12 inches (30 cm.) deep, n-ith a bare for the blower; and (3) sample trays 18 inches (46cm.) square and 6 inches (15 em.) deep. The trays are squaw frames having bottoms of clieesecloth over screen wire lreld i n place by cleats. I n use the trays are placed on top of each other over the open end of the baffle box. This drier takes advantage of the rapid movement of a large volume of air through the material, 15-hich presents a large surface of exposure. The lower the humidity the faster is the rat,e of drying. I n a number of iiistances of drying wet niaterials the temperature of the material has been noted as being as low as 46" F. (8" C.), the teriiperature of an ice box. The reduction of the temperature permit's the drying of perishable materials with little or no chemical change. It has been possible to dry diced fresh potatoes, sugar beets, and 1
Received February 24. 1930.
mangel beets with hut little if aiiy oxidase reaction, mid the dried ground sample was almost white. That the drying of materials in this apparatus does Il(Jt allow any appreciable changes iii the nitrogen compounds Irabeen observed in the cai;e of bovine feces. S o loss of n i t r o p i was obsermd, nor n-as there any change i n the true aiid ii011protein nitrogen. For the drying of yery wet. sticky. or past c*loth-iiottomtrays are not suitable, and a 1ion.n in Figure 2: has been found practical. This box has a bottom of cheesecloth aiitl screen wire as d i m the trays. One side of the box ha,.; a door for the introductioii and reinoval of the glass plate.. The glass plates are ataggered bo that the air must pass over (Jlle after the other. .Ifter the material lias lost its xticky characteristics it is hcraped from the plates onto the cloth of the hottoin ( ~ ftllc, h x , where it has greater exposure to the air current.
Figure 2-Drier
for Wet Materials
This plate arrangemerit has heeii f o i i i i d excelleiit f i i r tlw drying of ground lean meats for animal-feeding a room temperature of 72" F. (22" C.)and humidity of 44 per cent it has been possible to dry ground lean meat to a dryric+ that permitted grinding in a burr niill in less than 20 bows. The temperature of the meats, under these room coiiditioii.-. during the reinoval of the major portion of the moisture Irabeen ohserl-ed to be as l o x as 48" F. (9" C.)>averaging ai)proximately 50" F. (10" C.). The dried meats have had tlic fresh odor of the raw material. This drying apparatus lias been duplicated by other workers, who have reported favorably regarding it. The writer lias had oiie in use for more than eight years.
