15 



REPORT 



BY 



DR. J. A. MARKER 

 ON OBSERVATIONS MADE AT THE NATIONAL PHYSICAL LABORATORY 



I'l'iiX THB 



TEMPERATURE OF SOLIDIFICATION OF THE MERCURY IN THERMOMETER No. M.O. 30. 



The thermometer was compared with a standard under the most favourable conditions obtainable with 

 the present apparatus, in a vacuum vessel in acetone, cooled by adding solid CO-,. 



The stirring was found to be absolutely essential when readings to any considerable accuracy were 

 required. 



As our own mercury standard Tonnelot only reads to - 40 C., and comparisons were wanted to the 

 actual freezing-point of the mercury in the thermometer to be tested, the standard chosen was a toluene 

 Tonnelot thermometer. 



For this instrument it was not convenient to have complete immersion, so an emergent stem correction, 

 amounting to '2 F., has been applied when necessary. 



The thermometer M.O. 30 was tested down to the point at which its mercury solidified. 



This point was determined six times. The lowest temperature reached before solidification was 

 - 45 '5 F., on its own scale, and the highest about - 44 F. It was clamped independently of the stirrer, 

 so as to be affected as little as possible by its vibration. During the whole time solid C0 2 was added in 

 small quantities to prevent rise of temperature during the readings. 



The corrections, as determined under these conditions, were as follows, the toluene readings being 

 reduced to the hydrogen scale : 



CORRECTION. 



At - 38 F. 0-0 Freezing-point 32 -3 F. 



- 40 F. - 1 



-41 F. -0-3 



-45F. -0-4 



The readings could not be made by telescope, and the divisions are only about 1'3 millims. to 1 F., 

 and the thermometer is divided into whole degrees. 



No perceptible difference appeared in the indication at the freezing-point of mercury ( - 38 F.) of the 

 thermometer before and after its mercury had been frozen. 



After the freezing of the mercury the thermometer was taken out of the liquid as quickly as possible, 

 and, on the last occasion, the thawing of the mercury in the bulb took place probably before the capillary 

 neck had been quite freed from solid, and the bulb was broken, thus rendering impossible the observations 

 contemplated at the higher ranges. 



The freezing-point of mercury as deduced from 



Mercury Tonnelot 11562= -37'98F. 

 Toluene 71042 =- 37- 96 F. 



