10 BULLETIN" 451, U. S. DEPARTMENT OF AGRICULTURE. 



over sediment for 74 clays, during which time a considerable quantity of 

 crystals formed, the supernatant liquid was decanted and analyzed. The bottle 

 was then filled with water, the sediment broken up, and the corked bottle 

 mechanically shaken for several hours. The supernatant liquid was in turn 

 decanted, and the sediment, which still contained orange crystals, was once 

 more extracted in the same way. The values of x in M 2 Sx were found as 

 follows : Original solution, 4.33 ; first extract, 4.17 ; second extract, 4.04. Using 

 the thiosulphate figures as an index of the amount of mother liquor remaining 

 in each extract gave x=3.75 for the CaSx of the original crystals and x=3.97 

 'for the crystals remaining after the first extraction, though these figures must 

 of course be regarded as only approximations. 



Experiments 1 and 3 had seemed to show that the use of an excess 

 of lime necessarily produced in the fresh preparations a distinctly 

 plus reaction figure and a considerable proportion of tetrasulphid. 

 But the preparations there made had been rather intimately mixed 

 with their sediments during and after cooling under conditions not 

 entirely comparable to the ordinary. Accordingly, further experi- 

 ments were undertaken. 



EXPERIMENT 10. 



Preparation K, already mentioned under Experiment 7, made with excessive 

 lime, after boiling for 1.5 hours, was allowed to cool slightly under gas, mixed, 

 allowed to settle a moment, and then decanted from most of the sediment into 

 a 200 c.c. stout flask which was filled almost full and stoppered. The flask was 

 immersed in a water bath set on the steam bath and left at rest for about 

 0.75 hour at 70° to 75° C. The still slightly cloudy solution was decanted 

 through cotton, through which it filtered perfectly clear. After about two 

 hours, when the solution had become thoroughly cold, an 8-volume dilution 

 showed a reaction figure of — 0.02 and a value of x in M 2 Sx=4.40. 



Sample Q was prepared in the regular apparatus with excess lime, but boiled 

 for only 0.25 hour. After cooling five minutes under gas with frequent shaking 

 sediment and all were brought onto a cotton filter, except for a portion of 

 mixed sediment and liquid separately preserved. In about three hours crystals 

 had formed in the sediment of the unfiltered material, but none appeared then 

 or after several days in the filtered solution. A portion of the latter, about 

 three hours after preparation, was diluted to eight volumes, and the diluted 

 solution showed a reaction figure of +0.47 with a value of x in M 2 Sx of 4.77. 

 The concentrate contained 2.95 per cent monosulphur. 



As respects reaction figures, it is evident that a preparation car- 

 rying excess of lime, if cooled in intimate contact with its sediment, 

 will very naturally possess a plus reaction figure. But if the prepa- 

 ration is allowed to settle in the heat, undissolved calcium hydrate 

 is rapidly deposited and so removed from further activity, while the 

 small amount remaining in solution soon disappears through reac- 

 tion with pentasulphid. Hydrolysis will finally produce a minus 

 reaction figure. The latter conditions of course more nearly parallel 

 those prevailing in practice. 



The marked difference in the values for x in CaS x shown by 

 Preparations P and Q is also of interest. It seems futile to speculate 

 on what particular polysulphid may be the immediate product of 



