294 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 13 
PROCEEDINGS OF THE ACADEMY AND AFFILIATED 
SOCIETIES 
WASHINGTON ACADEMY OF SCIENCES 
171ST MEETING 
The 171st meeting of the Acaprmy was held jointly with the Philosophical 
Society of Washington in the Assembly Hall of the Cosmos Club the evening 
of Thursday, December 21, 1922. Dr. H. A. Cuark, Physicist of the Taylor 
Instrument Companies, Rochester, New York, delivered an address entitled, 
The manufacture of thermometers. 
In the drawing of capillary tubing for thermometers, the workman fashions 
a mass of hot glass of approximately taffy-pulling consistency, on the end of 
a blowpipe. In this mass (12 to 16 inches long and 4 to 6 inches in diameter), 
the relative dimensions of the various parts in a cross section (such as the two 
diameters of an oval bore, if it is oval, and the various outside diameters if 
the tube is not cylindrical) are the same as in the completed tubing. It is 
_then drawn mechanically to a length of about 180 feet, the final diameter 
depending upon various factors including rate of drawing. 
To make a ‘“‘chemical” thermometer, the workman starts with a piece of 
capillary cut to length, the area of bore of which has been carefully determined 
at both ends with a high power microscope. If it is to be a precision ther- 
mometer, the bore has, in addition, been calibrated with a mercury thread. 
A short piece of large-bore thin-walled tubing is sealed on for a bulb and its 
end drawn to a capillary through which mercury flows into the bulb, partly 
filling it, as it cools. The end of the bulb is sealed off, the mercury inside 
boiled to expel air, and the entire system now fills as it cools with the upper 
end of the stem under mercury. 
The upper end is now sealed off with a large ‘false chamber” into which 
the bulb filling flows when bulb and stem are put into an electric oven for 
annealing, temperature being carefully controlled. 
After annealing, excess mercury is driven into the false chamber and the 
stem is melted off just below, in such a way that the capillary space above 
the mercury column is evacuated or is filled with nitrogen, according to the 
range desired. 
The “tube,” so called, is now ready for a scale. For this purpose it is 
“pointed” by locating the mercury surface in the capillary at each of several 
known temperatures, by means of a fine scratch on the stem. To do this, 
the ‘‘tube”’ is immersed in well-stirred “baths’’ of various liquids, the tem- 
perature of each being determined with a standard thermometer. The 
temperature points chosen for pointing depend on the accuracy desired, as 
well as the range. 
The tube is coated with wax and an automatic engraving-machine cuts 
the graduations, the spacing being automatically varied as required by the 
slight unavoidable non-uniformity of bore. Dipping into hydrofluoric acid, 
cleaning off acid and wax, and filling graduations with pigment make the 
thermometer finally complete. 
The many other types of mercury-in-glass thermometers, clinical, indus- 
trial and others, pass through the above processes as well as others, depending 
upon the type. Still other types, consisting of liquid-in-metal bulbs and 
flexible metallic capillaries, much used in industry, cannot be here described 
for lack of space. (Author’s abstract.) 
