Found. 



Calculated. 



37-02 



37-41 



13-39 



13-34 



7-90 



8-34 



22-56 



22-51 



6-30 



6-26 



9-08 



9-79 



3-75 



2-35 



Chemistry and Physics. 415 



mineral must contain a small amount of impurity ; and a ser- 

 pentinous or chloritic molecule is the most probable admixture. 

 In the Port Henry mica the ratios are perfectly simple. 

 The formula, E /// 36 E V/ 46 K 18 H 38 (Si0 4 )6 1 5 F 2 , if we neglect the 

 small amounts of fluorine and excessive oxygen, reduces easily 

 to a mixture of the three typical molecules : 



Al 2 (Si0 4 ) 3 Fe" 2 KH, 

 Fe'"„(Si0 4 ) 3 Fe // o KH, 

 Al (SiOJ.Mg.KH,, 



in the ratio 2:1:1. This compares well with the analysis, 

 reduced as usual, thus : 



SiO 



Alo0 3 



FeA 



FeO 



McrO 



KoO 



H,0 



100-00 100-00 



Here the theoretical water is too low and the potash too high ; 

 both outside the allowable range of error. Their reciprocal 

 replacements explain the slight discordance only in part ; and 

 the nature of the mineral suggests a small excess of water due 

 to incipient alteration. Altogether the agreement between 

 analysis and theory is remarkably close. 



[To be continued.] 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. On an improved Vapor-density Method. — The method pro- 

 posed by Schalt, for determining vapor-density depends upon a 

 comparison of the pressure exerted by a certain known amount 

 of gas let into the bulb and measured under normal conditions, 

 with that exerted by the vapor of the substance itself produced 

 by heating this bulb. Originally a measured volume of air was 

 passed into the bulb ; but he has now improved the method by 

 decomposing a weighed quantity of pure sodium carbonate within 

 the apparatus, and then comparing the pressure of the carbon di- 

 oxide evolved with that of the vaporized substance. The apparatus 

 consists of a long-necked flask, of 3 50 to 200cm 3 . capacity, hav- 

 ing a lateral tube near its mouth. This flask is supported within 

 a beaker containing the heating material, by a cork surrounding 

 its neck and resting upon a plate of asbestos, serving as a cover. 

 The lateral tube, which should be 10cm. above the bulb, is con- 



