Physical and Chemical Behavior of Solids. 241 



siderably from those usually quoted ; consequently it seems 

 advisable to consider these experiments in some detail. 



Spring investigated first* the effect of repeated alternate 

 compression and- pulverization on the reaction between barium 

 sulphate and sodium carbonate; and on the reverse action 

 somewhat later.f He described his methods in the following 

 words : " I have operated each time with about 1 gram of 

 material [a mixture made by shaking together 1 part BaS0 4 (or 

 BaC0 3 ) with 3 parts Ka 2 CO, (or Na 2 S0' 4 ), both powdered and 

 thoroughly dried]. The small cylinder obtained by compres- 

 sion [to 6000 atmospheres] was then pulverized as fine as pos- 

 sible and the powder was washed completely with cold water. 

 The insoluble residue, after being filtered off, was analyzed by 

 the ordinary procedure in order to determine its content of 

 barium carbonate." This process of alternate compression and 

 pulverization was, with some changes, repeated a number of 

 times in order to determine the effect of successive treatments ; 

 moreover, the cylinders after a given number of compressions 

 were allowed to stand at atmospheric pressure for periods of 

 time up to 28 days, and the amount of barium carbonate deter- 

 mined after treatment with water as above. The results are 

 brought together in the following tables : 



Table V. Percentage amount of BaS0 4 " transformed " into BaC0 3 (deter- 

 mined as above) by reaction with Na 2 C0 3 , under the stated conditions. 



Number of 

 "compressions " 



Tim 

 



3 of standing 



7 



thereafter in 

 14 



days 



28 



1 

 3 

 6 



0-94 



4-78 

 8-99 



1-60 

 6-78 

 9-94 



3-08 

 9-01 



10-89 



3-84 



9-15 



11-08 



Table VI. Percentag 

 into BaS0 4 by r 



e amount of BaC0 3 (determined as above) ' 

 eaction with Na 2 S0 4 , under the stated coi 



transformed" 

 iditions. 



Number of 

 " compressions" 



Time 

 



of standing 



7 



thereafter in 

 14 



days 





 1 

 3 

 6 



4979 

 59-16 

 69-25 

 73-31 



48-95 

 63-91 



74-98 

 80-68 



49-47 

 64-66 



77-38 

 80-31 







*Bull. soc. chim. (2), xliv, 166-9, 1885; Bull. Acad. Roy. Belg. (3), x, 

 204-8, 1885 ; Jahresbericht, 1885, 461. 



f Ibid. (2), xlvi, 299-302, 1886 ; Jahresbericht, 1886, xxxix. 



