IN MIXTURES OF ACETONE AND WATER. 101 



was drawn into the viscosimeter. The instruments were thus thor- 

 oughly and quickly dried, and examination with a hand-lens showed 

 complete absence of dust particles in the capillary or bulb tubes. 



When it was necessary to take a series of readings on a particular 

 viscosimeter, this was equipped with a special head designed to exclude 

 moisture and dust particles from contact with the liquid in the instru- 

 ment. The liquid was then raised to the upper mark on the small 

 bulb by means of a constant air-pressure apparatus, using the same 

 stand-pipe as the cooling system. Air entering the viscosimeter from 

 the pressure vessel was first carefully dried and freed from dust by 

 the use of fused calcium chloride and cotton wool, and by means of 

 stop-cocks all external air was excluded during the actual time of flow of 

 the liquid through the capillary. 



By observing the precautions noted above we have succeeded in 

 obtaining from 3 to 5 consecutive readings on any particular viscosim- 

 eter, all agreeing to within the limits of error of the stop-watch used, 

 which was a fine split-second Swiss instrument, reading to 0.2 second 

 and adjusted with great accuracy. This watch had the additional 

 advantage of running continuously, whether the hands were released or 

 not, and gave much better results than the intermittent form heretofore 

 used. Frequent comparisons were made with standard chronometers, 

 and no errors of sufficient magnitude to affect the accuracy of the work 

 were detected. 



Specific-gravity determinations were made with a modified form of 

 the Ostwald pycnometer, which is so well known that it does not 

 require further description. 



All flasks were carefully calibrated to hold aliquot parts of the true 

 liter at 20, and solutionswere brought to within 0.1 of this temperature 

 before being diluted to the mark. 



SOLVENTS. 



Water. The water was purified by the method of Jones and Mackay 1 

 as modified by Schmidt, and has a mean specific conductivity of 

 1.5XlO- 6 at25. 



Acetone. Kahlbaum's so-called pure acetone was allowed to stand 

 for several days over calcium chloride, and distilled two or three times. 

 No difficulty was experienced in obtaining a product of approximately 

 the same conductivity as the water used in this work. Solutions were 

 made up as quickly as possible after distilling the acetone, which was 

 always kept in a dark place. 



Mixtures of Acetone and Water. The mixtures used as solvents were 

 made by diluting a given volume of acetone to a definite volume with 

 water at 20. For convenience, the number of cubic centimeters of 

 acetone diluted to 100 c.c. was indicated as the " percentage" of acetone 

 in the solvent. A very considerable contraction takes place when ace- 

 tone and water are mixed, so that the figures used to designate the 



. Chem. Journ., 17. 83 (1895). 



