Section III, 1917 [129] Trans. R.S.C. 



A Sensitive Bath-Thermostat. 



By A. Norman Shaw, B.A. (Cantab.), D.Sc. 



(Presented by Dr. H. T. Barnes, F.R.S., F.R.S.C.) 

 (Read May Meeting, 1917.) 



1. Introduction. The thermostat is a well known laboratory 

 apparatus, and therefore in recording notes on the construction of a 

 simple type, a justification rather than an introduction is required. 

 Dr. H. L. Bronson and the present writer, while engaged on an investi- 

 gation of standard cells in 1909, constructed an oil-bath thermostat 

 which was a simplified copy of one described by Messrs. Wolff and 

 Waters,^ and later, while using it in connection with an absolute 

 determination of the voltage of the Weston standard cell, the writer 

 made some minor changes in its design. It was not considered at 

 that time, however, in view of the large amount of literature on 

 thermostats, that the matter was worth recording in the papers 

 published about these investigations; but since then, many inquiries 

 have been received concerning the details of its construction, and it 

 appears that the sensibility in regulation and constancy in behaviour 

 of our apparatus was considerably greater than is usually obtained 

 with a comparatively simple outfit. These notes are recorded, 

 therefore, as a possible aid, chiefly with reference to time and expense, 

 to any investigator who desires to construct a simple but sensitive 

 thermostat of this type. 



2. Construction. There are five main parts in this thermostat: 

 (a) the containing vessel, (&) the stirrer, (c) the heating coils, (d) the 

 thermo-regulator, and (e) the stands for supporting the objects to 

 be maintained at the constant temperature. 



The section on "The Comparing Baths" for standard cells 

 (pp. 33-39) in the paper by Wolff and Waters already quoted, should, 

 if possible, be read in conjunction with the following directions, the 

 diagrams there being particularly useful in showing a sample arrange- 

 ment of the electrical connections. 



(a) The containing vessel may be made conveniently out of two 

 circular wash tubs, one being placed inside the other. It is best to 

 choose a wooden tub for the inside and a metal one for the outside. 

 The wood is more suitable for making attachments with nails or 



iBull. Bur. Stand, vol. IV, p. 33, 1907. 



