WB. W. N. SHAW ON HYGROMETRIC METHODS. 145 



Endlich, nachdem ich drei Wochen daran mich abgemllht, schienen die Versuchs- 

 ergebnisse einigermassen entsprechend. Die . . flinfzig . . Versuche lieferten 

 alle eine zu kleine absolute Feuchtigkeit und zwar im Mittel um 2*5 mm. circa zu 

 klein." 



A similar apparatus was used by SWORYKIN, who seems to have had more success 

 with it 



An apparatus somewhat similar to SCHWACKHOFER'S was designed and made by 

 Mr. DINES. It is described in the 'Meteorological Magazine,' September, 1883, and 

 is said to work satisfactorily. 



The next instrument of the kind is EDELMANN'S, described in WIEDEMANN'S 

 ' Annalen,' vol. 6, 1870, p. 455. It is of very much simpler construction. A glass 

 cylinder is closed at each end with india-rubber corks perforated so as to take a tube 

 containing a thermometer and connected with a mercury pressure-gauge at one end, 

 and at the other a second tube communicating with the top and bottom respectively 

 of a small vessel of sulphuric acid by means of glass cone joints. The mercury gauge 

 is also attached to a cone joint ; there are stop cocks between the cone joints and the 

 cylinder. The cylinder is provided with a metal jacket. By the double connexion the 

 sulphuric acid is allowed to run into the cylinder without altering the volume of the 

 air. Between each operation the cylinder has to be cleaned and dried, and washing 

 out with alcohol and ether is recommended. It is said to give good results, though 

 none are quoted in the paper, and if, as suggested, the vessel is finally dried by passing 

 through it air from a " Wasser-trommel-geblase," good results ought certainly to be 

 received with unusual gratitude. The description of the instrument, and its use, 

 reads rather like an instrument maker's solution of the problem " to make an absolute 

 hygrometer." VAN HASSELT* has described an instrument somewhat similar to 

 EDELMANN'S, but he uses phosphoric anhydride instead of sulphuric acid. The 

 anhydride is enclosed in a thin glass bulb, which is broken by shaking when the 

 moisture is to be absorbed ; the difference of pressure is observed by means of an oil 

 manometer, which consists of two glass tubes connected by a flexible india-rubber one. 

 This arrangement allows the volume to be reduced to its original value before reading 

 off the pressure. 



RuDORFFt uses a WOULFF'S bottle, with three necks, in an ingenious manner. Into 

 the middle neck is fixed a burette, which supplies the sulphuric acid ; this is allowed 

 to pass into the vessel until the pressure reaches its original value, as indicated by a 

 manometer of sulphuric acid, sp. gr. 1'300. Thus the volume of sulphuric acid run 

 in gives at once the diminution of volume of the air due to the absorption of the 

 moisture. 



This plan was somewhat improved by NEESEN.J who has two WOULFF bottles, one 



* ' Beiblattor,' 1879, p. 697 

 t ' Beiblatter,' 1880, p. 349 

 J ' WIKDEMANN, Annalen,' vol. 11 1880, p. 526. 



MDCCCLXXXVIII. A. U 



