( 671 ) 



removing llie vapour uiuler veiy low pressure, which implies a 

 rather considei'able loss of work by friction, if boiling nevertheless 

 occurred at a higher pressure. And this nnist occur Avhen to the 

 suction i)i-essure was to be added a noticeable hydrostatic pressure 

 due to the turns of the condensationspiral, where the vapour forms, 

 being much beneath tiie surface of the evaporating liquid. In the case 

 of the methylchloride circulation it seemed to me that the obtaining 

 of the lowest possible temjierature was not of utmost importance and 

 that there was no objection to simplify the construction by allowing 

 liciuid to be introduced to a height of 20 cm. in tiie refrigerator, 

 though not all protit is taken in this way of the low ])ressure (at most 

 20 nmi. of mercury) under which the Burckhardt — Weiss vacuum 

 pump, which is introcbiced into the methylchloride circulation, sucks 

 at full speed (usually about 8 mm. is employed). 



The spiral where the ethylene is liquetied (length 53 m., inner 

 diameter 6.4 mm., thickness of wall 0.8 mm.) lies in two windings 

 in the hollow cylindrical mantel 6" in which the conical refrigerating 

 vessel D terminates below. There is just room between the two 

 windings of the spiral i^see section bottom left l)elovv^ and the elevation 

 of the section through I) bottom right on the plate) for the ascending 

 tube Ad by which the lower end of the inner spiral .Ic ^Ir/ is Joined 

 to the upi)er end of the outer. These two cylindrically wound spirals 

 are Joined to a Hat spiral Ac which lies on the bottom of the boiling- 

 vessel. When the latter is well tilled this spii-al lies Just under the 

 surface of the liquetied gas introduced through the cock .V. The spirals 

 are coupled so that the li(pii{l is driven out by the pressure of the 

 gas. If the boiling vessel is always kept so full that the tl at spiral is 

 immersed, it is advantageous to let out the condensed gas from the 

 last spiral. Shoidd it be desirable to work with a smaller quantity, 

 it is l)etter to tirst run the gas to be condensed through the tlat 

 s])iral ; this case is shown in the drawing. If the tlat sjtii-al is immersed 

 the temperature (usually — 87° C.) of the liquid can be read on the 

 thermometer (), the stem of which is bent for convenience and is 

 immersed in the tube Dj^ filjed with alcohol and protected from 

 interchange of teuq)erature with the air by means of aii ebonite 

 tul)e Dd-i Joined to it with tish glue. The capacity for liquetied gas 

 when the cylinder- and flat spirals are covered is 6 litei's, the volume 

 of tlie spiral 1 liter. 



The conical sjiace of the refrigerator is suflicieiit even foi' an 

 excessive boiling up of the li»]uid, which is always large at low 

 temperatui-cs as can be seen from the movements of the float. 



The regenei-ator spiral consists of two long tubes i>\ and i>V^ 31) m. 



