FROM WOOD V\l> i ii W,. 



the entire space enclosed within its exterior surface, including 



its pores and fissures. It is necessary, therefore, in determin- 

 ing the sp. o T . by the usual method of the hydrostatic balance, 

 to use some means for preventing tin- water from insinuating 

 itself into the pores and figures of such bodies as arc not of a 

 perfectly compact texture. [f the article employed for this 

 purpose be of a sp. u;r. different from water, and if (as will 

 almost always be the case) it protrude beyond the surface of 

 the body so as to enlarge the bulk, it will he necessaiy ool 

 only to know its weight in air. but its specific gravity : and even 

 then it is difficult to make a satisfactory correction of the water 



ight in consequence of the change which the article made 

 use of may sustain in its specific gravity by pressure in apply- 

 ing it to the body, and also, from the different specific gravity 

 of different parts of articles not expressly prepared for tin 

 purpose. 



A- it was necessary forme to determine with great accuracy 

 the specific gravities of dry wood, charcoal, and the mineral 

 coals, all of which absorb water and present more or less fissures 

 and as I wished to relieve myself from liability to inaccu- 

 racies from the sources which have been detailed, I determined 

 to make a compound which should be convenient to use, and 

 whose specific gravity should be precisely thai of wat< r al <><»° 



Fahrenheit. 



This was effected with white wax and yellow rosin; tin 

 specific ui.i\ ityof the former was .967, and of the latter i .0 ! 

 The compound was of the lust possible consistence, and 

 whether compressed by mechanical means at .1 l-iw tempera* 

 tore, or expanded by the temperature of water al 130°, it 

 would in either case he miit\ when broughl to the tempei 



.lire o! 1)11 '. and the whole mass was perfectlj uniform. 



The difficulty "i producing this compound was much gr< at. i 

 than had been anticipated-, and will he apparent, when it i~ 

 stated that the nn- weighed at tin- commencement ab iuI I 

 ounces, taken h\ arithmetical calculation in tin- proportions 

 supposed to be necessary, which were is irrains of rosiu to 100 



oiis of wax. and although the unallesl additions supposed 



\ oi.. in. — II 



