92 



Journal of Applied Microscopy. 



wise ground internally. The lower por- 

 tion of tube B has an internal diameter 

 of 2 mm., and when placed in position, 

 inside of part A, it should come within 

 one or two millimeters of the bottom of 

 the cup. In this case, the first droplet 

 of mercury, as it issues from below, 

 shuts off the. outflow of gas. This is an 

 important condition, and should be care- 

 fully seen to in the manufacture of a 

 good regulator. 



The upper part of part C is solid, 

 whereas the lower portion is hollow. 

 The gas enters through a large opening 

 (2) and passes down to 4, the minimum 

 outflow, and to 5 and out at 3. The 

 portion marked 6 is ground to fit exactly 

 the corresponding part in B. If this is 

 not done properly the minimum outflow 

 of gas cannot be regulated as perfectly 

 as it otherwise can be. The upper por- 

 tion of C is a ground stopper fltting into 

 B. 



The manipulation of the thermo-regu- 

 lator is very simple. The gas enters 

 through the upper lateral tube. If it is 

 desired to diminish the inflow of gas, 

 this can be done by turning B. The gas 

 passes through 1 into the inner space 

 and leaves at 2. As stated above, the 

 gas goes down, and a portion leaves 

 through the minimum supply opening 

 4, while the remainder passes down 

 through 5 and out at 3. By turning pari 

 C, the minimum outflow of gas can be 

 regulated at will. 



The regulator works exceedingly well, 

 especially when connected with a gas- 

 pressure regulator such as that of Mr. 

 Murrill, a description of which follows. 



Thermo-regulator of this type, excel- 

 lently constructed, can be obtained from 

 Greiner and Friedrichs, Stuetzerbach, 

 Thueringen, for about 8 marks.. 



Dr. F. G. Novy. 



From the Hygienic Laboratory of the Uni- 

 versity of Michigan, Ann Arbor, Mich. 



An Efficient Gas-Pressure Regu- 

 lator. 



It is well known that the various types 

 of mercury thermo-regulators cannot 

 compensate for marked changes in the 

 gas pressure, and for this reason it is 

 almost impossible to maintain a con- 

 stant temperature for any considerable 

 length of time with any degree of cer- 

 tainty. Numerous contrivances for regu- 

 lating the pressure have been devised at 

 various times, and several are to be had 

 from the principal dealers, but they 

 either fail entirely in their purpose, or 

 are impracticable for general use owing 

 to cost, difficulties of construction, or 

 other reasons. The apparatus of Moi- 

 tessier, as catalogued in this country and 



in Europe, appears to have some feat- 

 ures in common with the one here 

 described, but its cost bars it from gen- 

 eral use. The Giroud Rheometer, modi- 

 fied by Schiff, was tested in connection 



with a mercury thermostat, with results 

 to indicate it as useless for that pur- 

 pose. A pressure regulator made of 

 glass, described by Schiff,* is quite 

 similar in principle to the one here 

 described, but has the disadvantages of 

 being quite fragile, besides requiring 

 skilled glass blowing in its construction. 

 An apparatus by Knudsen is also 

 descrlbedt but it is too complicated 

 to be practical. 



Having experienced the same difficul- 

 ties that other workers nave, the 

 attempt was made to devise a simple 

 apparatus which would deliver gas at 



C*Oo J -SS C r/0'\/. 



constant pressure, regardless of the vari- 

 ous changes of pressure in the gas 

 pipes. The apparatus having proved 

 satisfactory, a description of it is given. 

 Its strong points are efficiency, simplic- 

 ity, durability, and cheapness. It can 

 be made of sheet metal, preferably of 

 copper, by any sheet-metal worker, or 

 may be obtained from the Eberbach 



* Ber. d. Chem. Ges. 1885, 2833; 

 Anal. Chem., 1886, 385. 

 t Ztschr. Anal. Chem. 1886, 383. 



Ztschr. 



