238 Johnston and Adams — High Pressures on the 



panied by an increase in volume. The effect of this is, in 

 Spring's experiments, not so important as it might seem to be ;- 

 for any gas formed could easily escape between the piston and 

 cylinder. Indeed this happened in one case at least, for he 

 states that on compressing a mixture of sodium carbonate with 

 arsenic oxide, much carbon dioxide was evolved, and a mass of 

 sodium arsenate remained. 



The bulk of the work along this line may be divided for 

 convenience into three classes : these will now be considered 

 separately. 



A. The Formation of Sulphides and Arsenides by 

 Compression. 



In a later paper* Spring describes experiments in which the 

 effect of repeated compression upon intimate mixtures of sul- 

 phur with a number of metals was investigated. The method 

 was as follows : " The powder [obtained by mixing flowers of 

 sulphur with filings of the metal] is submitted to a first com- 

 pression of 6500 atm., whereupon it is transformed into a com- 

 pact hard mass, microscopic examination of which shows that 

 the reaction has taken place wherever the elements were in 

 contact. This mass is then reduced to fine powder by means 

 of a file, and this powder in turn is compressed again. This 

 maneuver is repeated until the result is such that microscopic 

 examination shows no trace of free metal or of free sulphur. 

 Generally two or three compressions are sufficient to yield a 

 perfect result ; except that for the hard metals which have 

 little affinity for sulphur, six or eight further compressions 

 may be necessary." The results obtained, as given by Spring, 

 are summarized in Table IV. 



In another paperf he describes similar experiments resulting 

 in the combination of arsenic with zinc, lead, tin, cadmium, 

 copper and silver and the alleged production of homogeneous 

 crystalline blocks. 



Spring repeated certain of these experiments before Friedel, 

 who writes :J "These experiments made before me by M. 

 Spring prove that combination occurs between certain sub- 

 stances under the conditions under which he operates ; that is 

 to say, mixture of powders, compression, then pulverization 

 again, followed anew by compression, and so on several times 

 in succession. . . . For zinc sulphide, the change of color 

 of the mixture seems to me a more certain indication of com- 

 bination than the evolution of sulphureted hydrogen by the 

 action of hydrochloric acid : for I have since found that 



*Bull. soc. chim., xxxix, 641-7, 1883; Bull. Acad. Koy. Belg. (3), v, 

 492-504; Ber., xvi, 999, 1883; Jahresbericht, 1883, 29. 



f Ber., xvi, 324, 1883 ; Bull. Acad. Roy. Belg. (3), v, 229-36, 1883 ; Jahres- 

 bericht, 1883, 28. 



% Bull. soc. chim., xl, 528, 1883. 



