308 M. Beketoff on the Displacement of some Elements by others, 



spheres after several days ; under 6 atmospheres there was a 

 feeble but distinct reduction of silver ; and under 14 atmospheres 

 dark-violet silver was deposited even on the next day. A 

 solution of 1 part of sulphate of silver in 50 parts of water exhi- 

 bited no decomposition under a pressure of 14 atmospheres, but 

 it did under a pressure of 23 atmospheres. 



Experiments with Carbonic Acid. — A 12-per-cent. solution of 

 acetate of lime was enclosed in a tube with marble and hydro- 

 chloric acid. When the pressure of the carbonic acid given off 

 amounted to 14*5 atmospheres, no action was perceptible. Under 

 27*5 atmospheres there was, after a few days, a separation of 

 carbonate of lime. In a saturated solution of acetate of lime 

 carbonate of lime was precipitated under a pressure of 28 - 5 atmo- 

 spheres. The latter appears in these cases, when seen under the 

 microscope, as globular aggregates of acicular crystals. In- 

 versely, marble was sealed up with excess of dilute acetic acid. 

 In a few days the pressure rose to 17 atmospheres, but did not 

 further increase even after eight months. Part of the marble 

 remained undissolved. Hence the decomposition of marble by 

 acetic acid stops at pretty much the same temperature as that 

 at which the decomposition of acetate of lime by carbonic acid 

 stops. 



A dilute perfectly neutral solution of chloride of calcium was 

 not changed under a pressure of 45 atmospheres (the tube in 

 this case contained condensed liquid carbonic acid); nor was 

 acetate of baryta under 30 atmospheres, or chloride of barium 

 under 60 atmospheres. 



The author's experiments on the reducing-power of zinc and 

 aluminium at high temperatures are known from previous com- 

 munications. Whereas aluminium readily sets free barium, it 

 does not reduce calcium from oxy chloride of calcium. Alumi- 

 nium can in turn be separated by magnesium (from artificial 

 cryolite for instance) . If caustic potash is heated in a gun- 

 barrel with aluminium, globules of potassium are readily obtained. 

 This reaction may perhaps be applicable in practice. 



In almost all cases of the displacement of metals by others, 

 the author found that the element with lower specific gravity 

 expels the one with higher. This rule of course applies only to 

 elements that are chemically analogous. Such, however, the 

 true metals are, and metallic solutions are therefore well adapted 

 for testing the above rule. From Fischer and Odling's experi- 

 ments, a Table may be deduced for the metals, in which each 

 element is replaced by each preceding one. 



