8 BULLETIN 451, U. S. DEPARTMENT OF AGRICULTURE. 



calcium sulphite added to boiling dilute solutions reacts with poly- 

 sulphur and forms thiosulphate. Therefore in practice there must 

 be a fairly definitely fixed concentration below which sulphite will 

 not be permanently formed in significant amount during the prepa- 

 ration of lime-sulphur solutions, lying somewhere between 3.04 and 

 5.63 per cent of monosulphur. It seemed desirable to fix this critical 

 concentration a little more closely. 



EXPERIMENT 7. 



Preparations of intermediate concentration were prepared in the usual man- 

 ner except that a decided excess of lime was used and boiling continued for 

 1.25 hours or longer. Preparation K was found to contain 3.33 per cent mono- 

 sulphur with a ratio M 2 Sx : M 2 S 2 03=1.82. Preparation L contained 3.95 per 

 cent monosulphur with a ratio M 2 Sx : M 2 S 2 3 =3.79. 



By this experiment, in addition to which further tests did not seem 

 worth while, the critical concentration lies between 3.33 and 3.95 per 

 cent monosulphur, which, assuming that one-sixth of the sulphur is 

 converted to monosulphur, corresponds in the formula to the use of 

 respectively 20 and 23.7 grams of sulphur per 100 c. c. of finished 

 solution. 



RATIO OF POLYSULPHID TO THIOSULPHATE. 



For many years it has been unquestioned that the primary reac- 

 tion between lime and sulphur in water is: 3Ca(OH) 2 -f-(2x-j-2)S= 

 2CaS x -|-CaS 2 03-j-3H 2 0, which equation of course calls for a ratio of 

 2 between the molecules of polysulphid and thiosulphate produced. 

 The ratios actually obtained in Experiment 2, as already noted, all 

 fell considerably below the theoretical figure. Part of the dis- 

 crepancy may be ascribed to hydrolysis with subsequent loss by 

 volatilization of the hydrogen sulphid, and part to oxidation, since 

 the conditions of the experiments were only such as to minimize, not 

 absolutely exclude, contact with air. It seemed desirable to ascer- 

 tain how nearly the theoretical ratio could be reached under more 

 favorable conditions. 



EXPERIMENT 8. 



A fifth of the formula 45 :100 :1014 was charged into a stout bottle, the small 

 remaining space being filled with washed illuminating gas, and the tightly- 

 stoppered bottled was attached to a shaking machine and immersed in a water 

 bath. After heating for 0.5 hour the originally cold both had reached a tem- 

 perature of 80° C. and the liquid in the flask had become decidedly yellow. 

 Further heating rapidly deepened the color until after 0.75 hour from the start 

 a temperature of 95° C. was reached, after which the bath was maintained at 

 90° to 95° C. for one hour longer. The bottle was then removed from the bath 

 and cooled in running water. When it was opened the odors of illuminating 

 gas and of hydrogen sulphid were strong. A 4-volume dilution was made the 

 next day and analysis gave the molecular ratio M 2 S* ; M 2 S 2 0s=l.S9. (Prepara- 

 tion M.) 



