APPENDIX. 519 



From the third table (or last table) I find that the atomic 

 weight of oxalic acid crystals is 9 ; consequently, 90 is equi- 

 valent to ten atoms. From the table of carbonates I find that 

 the atom of bicarbonate of potash is 12-625. Consequently, 

 126-25, or ten atoms, is the quantity that would be required, 

 if the bicarbonate contained only one atom of water ; but, as it 

 usually contains 1^ atom of water, 131-875 grains will be re- 

 quisite. 



Fourth example. Suppose I wish to prepare oxalate of zinc 

 by double decomposition, from oxalate of ammonia and sul- 

 phate of zinc, what are the relative quantities of these two salts 

 in crystals that must be used ? The atomic weight of oxalate 

 of ammonia is 8-875, and of sulphate of zinc 18-125. Conse- 

 quently, we have only to take any equimultiples of these num- 

 bers ; for example, 



88 -75 grains oxalate of ammonia, 

 181-25 grains of sulphate of zinc. 



Dissolve these two salts in different portions of water, and mix 

 the solutions. The whole oxalic acid and oxide of zinc will 

 precipitate in combination, and nothing will remain in the li- 

 quid but a neutral solution of sulphate of ammonia. 



These are only a few of the numerous uses to which these 

 tables may be applied. It is obvious enough that if these tables 

 were laid down upon a sliding rule, after the manner of Dr. 

 Wollaston's scale of chemical equivalents, all these problems 

 would be solved at once by adjusting the slide, without any 

 arithmetical operation whatever. But the great multiplicity of 

 substances, amounting to several hundred, would of necessity 

 render such a scale so confused, that more time would be lost 

 in looking for the substances, than in performing the arithmeti- 

 cal calculations from the tables. 



Kk<i 



