and Laboratory Methods. 



1965 



it brings to the minds of those who see it resolve a " valuable resource " into 

 common silt, or something of the sort, and thus satisfy the beholder without 

 argument, explanation, or correspondence that further expense and labor on the 

 development of that particular resource is futile. Though less useful than the 

 pocket magnifier, it is nevertheless an important instrument in the kit of the 

 field geologist. Erwin Hinckley Barbour. 



University of Nebraska. 



c=o 



An Easily Constructed Thermostat. 



Those who attempt to regulate the temperature of water-baths, incubators, 

 etc., which require a rather low degree of heat, nearly always experience 

 considerable difficulty if the ordinary Reichert thermostat is used. The mer- 

 cury reservoir in this form of instrument is too small and the pinhole escape for 

 the gas from the inlet pipe far too large to admit of the rapid and accurate regu- 

 lation necessary for many kinds of work. 



After struggling with this problem for some time, the 

 writer devised a very efficient and inexpensive form of instru- CcT:.---a. 



ment which may be easily constructed by anyone of average 

 ability. The principle is, of course, the familiar one, but 

 the method of construction is new. 



The body of the instrument is an ordinary sideneck test- 

 tube. One should be selected of rather thick glass and as 

 large as can be taken by the tubulature of the water bath. 



From a one-hole soft rubber stopper which fits the test- 

 tube snugly, cut off about 10 mm. from the lower end and 

 into it fit a piece of tubing of about 4 mm. internal diameter 

 and about 75 mm. length (e, Fig. 1). Carefully push the 

 plug thus formed down into the test-tube until it reaches a 

 point about 40 mm. from the bottom {/, Fig. 1). In case 

 the stopper does not fit closely enough, a small quantity of 

 melted paraffine poured in will remedy the fault. 



The inlet tube {a, Fig. 1) is more difficult to make, and, 

 unless one is expert, some practice must precede the making 

 of a perfect one. The lower end of the tube should end in 

 a long, straight, slender point, and the pinhole by-pass should 

 be as small as it can possibly be made. It is best to begin by 

 drawing out the tube to make the point. Select a tube about 

 5 mm. diameter or less and, at a convenient distance (120 

 mm.) from one end, heat it strongly in the flame of an 

 ordinary Bunsen burner. When it is thoroughly soft, re- 

 move it from the flame, and at the same instant draw it out 

 into a slender thread. A few attempts will probably result 

 in a satisfactory tube and one can now pass to the more 

 difficult operation of blowing the pinhole. 



Fig. 1. — a, Inlet tube 

 for gas. b, Rubber 

 stopper, c, Pinhole 

 by-pass. d, Outlet 

 tube for gas e, 

 Tube in which the 

 mercury rises and 

 falls. /. Rubber 

 stopper, g. Cistern 

 filled with metallic 

 mercury. 



