6 BULLETIN 451, U. S. DEPARTMENT CE AGRICULTURE. 



On the ether hand, boiling for 0.25 hour was plainly insufficient. 

 All percentages are lower and so is the value of x in M 2 S X , while the 

 original reaction figure before storage was positive (Table 1). 



Next came a study of the effect of varying the concentration at 

 which the boiling was conducted. 



EFFECT OF VARYING CONCENTRATION. 



EXPERIMENT 5. 



The concentrates were prepared as described for the previous experiments, 

 and the results are given in Table 2. Preparation H was boiled only 0.75 hour 

 since the odor of hydrogen sulphid had then become very strong and Experiment 

 4 had shown no essential difference between boiling for 0.5 and one hour. In 

 case of Preparation I the ingredients made such a thick mixture that the 

 flask was first heated for 0.75 hour in a boiling-water bath with frequent shak- 

 ing and constant passage of alkali-washed illuminating gas, then the prepara- 

 tion was finished by boiling for 0.5 hour in the usual way. Preparation B, Ex- 

 periment 3, is also to be included in this group, being the middle member of 

 the series. 



The more dilute preparation. Preparation H. showed results en- 

 tirely comparable with Preparation B (Experiment 3). The appar- 

 ently lower value for x in M 2 S X is due to the relatively larger amount 

 of hydrogen sulphid. Assuming free H 2 S, the value of x in CaS x 

 is 4.94; assuming Ca(SH) 2 it becomes 5.09. 



In case of the more concentrated preparation, Preparation I, there 

 is evident a striking rise in the molecular ratio of polysulphid to thio- 

 sulphate. This well-known phenomenon in the preparation of highly 

 concentrated solutions has been ascribed by Van Slyke et al. 5 to the 

 decomposition of calcium thiosulphate into calcium sulphite and 

 sulphur. Notwithstanding the additional amount of sulphur thus 

 rendered available the value of x in M 2 S X suffers a distinct drop 

 in comparison with Preparations B and H, rendered more noticeable 

 if calculations are made to actual CaS x . Parallelly, Kiister and 

 Heberlein 6 found the A'alue of x in Na 2 S x to be highest at a certain 

 optimum concentration, decreasing when the solution was made either 

 more concentrated or more dilute. 



A question which here naturally arises is whether there is any 

 more complete utilization of the raw materials at one concentration 

 than at another. This can be answered approximately by comparing 

 the weights of monosulphur in Preparations H, B, and I. Letting 

 W stand for the weight of monosulphur, and v for the volume of 

 dissolved substance, the three following equations hold: 



(1) for Preparation H; W=.0161 (v+1014) 



(2) for Preparation B; W=.0304 (v+ 514) 



(3) for Preparation I; W==.0563 (v-f 264) 



