510 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Cottrell's results could not have been serious. On the other hand, a 

 temperature just below redness, perhaps 450°, obtained with a carefully 

 watched naked flame, and applied after long drying at lower temperature, 

 was capable of driving off in five minutes so much of the water that sub- 

 sequent similar heating for a quarter of an hour showed only an average 

 loss of 0.2 milligram. The product was wholly soluble in water, showing 

 that no decomposition of the sulphate itself had occurred. 



The manganous sulphate was purified with great care, and the crystals 

 employed were coarsely powdered. The specimen whose solubility was 

 to be determined was put into a large stout test-tube with a carefully 

 cleaned rubber stopper, and was kept for at least four hours at the 

 desired temperature in an Ostwald thermostat before a sample was 

 taken. The agitation of the mixture was active and continual, being 

 effected by an apparatus similar in principle to that of Schroder.* The 

 motive power was a Henrici hot-air motor. At the close of the ap- 

 pointed time the sample to be analyzed was removed by an effectual 

 filtering pipette, somewhat similar to one which has since been used 

 in van't Hoff's laboratory. f A diagram of the pipette is appended. 



Filtering Pipette. 



The filtering attachment, filled with cotton wool ("absorbent cotton," C), is tem- 

 porarily attached to the jet A of a 5-c.c. pipette by means of the rubber tube B. 



The cotton was very necessary to filter off the fine powder which ap- 

 peared during the stirring. In order to avoid change of temperature, 

 the pipette was previously warmed by placing it in a dry test-tube im- 

 mersed in the thermostat. Only the mouth of the test-tube was allowed 

 to project above the water of the thermostat, and of course every pre- 

 caution was taken to obtain a fair sample of the solution. 



After filling the pipette and quickly removing the rubber filtering-jet 

 attached to it, the clear solution was run into a weighing-bottle and was 

 quickly stoppered and weighed. The known amount of solution was 

 washed into a roomy platinum crucible, when it was cautiously evaporated, 



* Schroder, Zeitschr. phys. chem., 11, 454 (1893); Noyes, ibid., 9, 606 (1892). 

 For details see Richards and Faber, Am. Chera. Journal, 21, 168 (1899.) 

 t Van't Iloff and Meyerhoffer, Z. phys. ch., 27, 79 (1898). 



