IN POPULAR CHEMISTRY. 85 



air, and % = - 4 \ from the water. (See process of manufacture, 

 Chemistry, p. 106.) Hence, ^ (O) and ^ (R)=& of the acid, 

 was furnished by the water & of lf. tons = ^ ton (H 2 O). 



1 J. Hoiv much O in a Ib. 



f f of any quantity of sulphuric acid are O ; ? V is H ; and 

 If are S. Hence, in 1 Ib. of H 2 SO 3 there are ff Ib. (O). 



16. State the analogy between the compounds of O 

 and S. 



O. 



H 2 O. 



H 2 O 3 (hydrogen dioxide). 



CO.. 



S. 



H 8 S 2 . 

 CS 2 . 



The corresponding compounds possess not only an analo- 

 gous composition, but also similar chemical properties. 



1 48 ! fn the experiment with Na z SO, on page 

 an accurate thermometer will show that in making the so- 

 lution, the temperature of the liquid will fall, and in its 

 solidification, will rise. Explain. 



(See Popular Physics, p. 250.) 



Energy of temperature is absorbed in doing the work of 

 overcoming molecular cohesion ; hence, the thermometer falls 

 while the salt is becoming liquid. In returning to the solid 

 state it gives out this energy again as temperature. 



2. If, in making a solution of Na s SO^, ive use the salt 

 which lias effloresced, and so become anhydrous, the tem- 

 perature will rise instead of falling as before. Explain. 



This is because a solid hydrate is formed before the salt dis- 

 solves in the H 2 O. The same holds true of other anhydrous 

 bodies, as the chlorides of Zn, Fe, and Cu. 



3. IVliy is KNOg, used instead of NaNO^ for making 

 giuipowder ? 



Sodium nitrate is imported from Chili in large quantities, 

 and attempts have been made to use it for making gunpowder,* 



* Gunpowder is an intimate mechanical mixture of about 1 part niter, 

 1 part sulphur, and 3 parts charcoal. These proportions, however, vary 



