340 PBOCHHDEfOfl Of TIIK AMKKICAN ACADEMY. 



th.' results of 1 1 1 * * Kecktnann instrument with another carefully standard- 

 ized Donnal thermometer which had been directly compared with the 

 Standard of the Keichsanstalt. Accordingly another one was ])rocured. 



:;. Normal thermumeter No. 51-', Kichter (Jena glass, 59*^. This 

 thennometer was 65.5 cm. long ; the whole scale between 0° and loo° 

 was divided into one-tenth degrees. The scale it.self had a length of 

 57 cm. This instrument was tested with the greatest care in the 

 Keichsanstalt, not only as regards its calibration and behavior under 

 pressure, but also as regards the exact position of particular points, 

 especially the point 59.090°. This was found to read upon this 

 thermometer 58.330°, referred to the hydrogen standard, after cor- 

 rection for the ice point and for external pressure; the error here 

 being +0.240°. 



The observed values for the transition point in question, determined 

 with the third thermometer, and also the correction for the tempera- 

 ture of the thread, external pressure, and position of the ice point, are 

 to be found in Table II. Further, in that table are given the exact 

 temperature computed in terms of the hydrogen scale, and also the 

 control determinations made simultaneously with the Beckmann ther- 

 mometer. The errors of the small extra thermometers for the thermo- 

 stat, etc., were also carefully determined at this point in their scales. 



In order to carry out the determination of the transition temperature 

 with a mercury thermometer, it is necessary to have the stem of the 

 thermometer at the same temperature as the bulb. With high tem- 

 perature the error, due to neglect of this precaution, may be very great 

 In determining a transition temperature, it is impracticable to immerse 

 the whole thermometer in the melting mixture ; therefore some other 

 device is necessary in order to maintain the thread of the thermometer 

 at the right temperature. In the past we have used two devices for 

 this purpose. In one case the thermometer was surrounded by a glass 

 tube, through which circulated water of the right temperature. This 

 device works very well, except that it is diilicult to prevent cooling of 

 the water. The other device consisted in a deep thermostat, above 

 which the thermometer just projected. In the present series of deter- 

 minations we have altered this latter arrangement by making the 

 thermostat of glass, using a very tall glass beaker 52 centimeters in 

 heighl and 11 centimeters in diameter, surrounded at the sides with 

 asbestos paper and with long narrow windows in front and behind for 

 observation. A sketch of this apparatus is given in the accompanying 

 diagram. Into the water was immersed, quite to its top, a strong, very 

 large tube (A) closed below, of about 5 centimeters diameter. In this 

 there was contained, isolated by pieces of cork, the slightly smaller 



