of Compound Bodies. 417 



quantity of water ; or it is susceptible of condensation by pres- 

 sure; therefore the real gravity of lime is higher than that which 

 is assigned to it. Such substances should be weighed in oil, 

 alcohol, aether, a saline solution which has no action upon it, 

 or other liquid which will fully penetrate into the pores ; and 

 in some cases there may be occasion to place the liquid with 

 the solid matter immersed in it under the exhausted receiver 

 for a few minutes, to abstract the air, which is powerfully re- 

 tained by the pores. 



The other error arises from the formula which Hassenfratz 

 has employed. This formula I have not seen : the following 

 is that which I have used. 



Let m and n represent the weights of two substances ; a and 

 b their specific gravities; c the gravity of the compound: the 



11 mb -\- na , ^ . 



A = — : but smce 



6 ao 



the specific gravity of a mass of matter = -. ; — rr- — 



*^ o J itssp.gr. mb-\-na 



= c; which is the same w^ith Newton's. If the specific gravity 

 of one of the ingredients be required, we have by transposi- 



volume of the compound = 



tion, b = 



The following table exhibits the com- 



m-\-n . a—mc 



puted specific gravity of some metallic sulphurets by Hassen- 

 fratz ; their true specific gravity ; and that computed by the 

 formula just quoted. 



Sulphuret of 



Silver 



Mercury 



Iron 1st 



2nd 



Lead 



Bismuth 



Antimony .... 

 Arsenic 1st... 



2nd.. 



Molybdenum 



a s 



..- a 

 = >. 



CXI . 



£ ^ Nl 



9-22 

 11-83 

 5-62 

 4-73 

 10-06 

 8-65 

 5-53 

 7-05 

 7-05 

 5-97 



True 

 Gravity. 



7-2 

 10-0 

 4-518 

 4-83 

 7-0 

 6-131 

 4-368 

 3-225 

 5-315 

 4-73 



o S.S 



6-79 



9-4 



3-7 



3-0 



6-9 



5-7 



4-2 



4-6 



3-6 



3-5 



The first three columns are copied from Thomson's Che- 

 mistry, vol. iii. p. l.'iG, edit. 1817. 



From the computed numbers of Hassenfratz, it would ap- 

 N. S. Vol. S. No. 30. June 1829. 3 li pear, 



