COMPOUNDS OF CARBON WITH OXYGEN AND NITROGEN 387 



contain silica and the oxides of various metals ; amongst others, 

 the oxides of aluminium, calcium, and sodium. Water charged 

 with carbonic acid dissolves both the latter, transforming them into 

 carbonates. The waters of the ocean ought, as the evolution of the 

 carbonic anhydride proceeds, to precipitate salts of lime ; these are 

 actually found everywhere on the surface of the ground in those places 

 which previously formed the bed of the ocean. The presence of car- 

 bonic anhydride in solution in water is essential to the nourishment 

 and growth of water plants. 



Although carbonic anhydride is soluble in water, yet no definite 

 hydrate is formed ; u nevertheless an idea of the composition of this 

 hydrate may be formed from that of the salts of carbonic acid, because 

 a hydrate is nothing but a salt in which the metal is replaced by; 

 hydrogen. As carbonic anhydride forms salts of the composition 

 K 2 C0 3 , Na 2 C0 3 , HNaC0 3 , &c., therefore carbonic acid ought to have 

 the composition H 2 C0 3 that is, it ought to contain C0 2 + H 2 O. 

 Whenever this substance is formed, it decomposes into its component' 

 parts that is, into water and carbonic anhydride. The acid properties 

 of carbonic anhydride 11 bi3 are demonstrated by its being directly ab- 

 sorbed by alkaline solutions and forming salts with them. In distinction 

 from nitric, HN0 3 , and similar monobasic acids which with univalent 

 metals (exchanging one atom for one atom of hydrogen) give salts such 

 as those of potassium, sodium, and silver containing only one atom of the-- 

 metal (NaN0 3 , AgNO 3 ), and with bivalent 12 metals (such as calcium, 

 barium, lead) salts containing t wo acid groups for example, Ca(N0 3 ) 2 , 

 Pb(N0 3 ) 2 carbonic acid, H 2 C0 3 , in bibasic, that is contains two atoms 

 of hydrogen in the hydrate or two atoms of univalent metals in their 

 salts : for example, Na 2 C0 3 is washing soda, a normal salt ; NaHC0 3 ia 

 the bicarbonate, an acid salt. Therefore, if M' be a univalent metal, 

 its carbonates in general are the normal carbonate M' 2 C0 3 and the 



The crystalluhydrate, CO 2 ,8H 2 O of Wroblewski (Chapter I., Note 67), in the first 

 place, is only formed under special conditions ; in the second place, its existence still 

 requires confirmation ; and in the third place, it does not correspond with that hydrate 

 HjCOj which should occur, judging from the composition of the salts. 



11 bls It is easy to demonstrate the acid properties of carbonic anhydride by taking a 

 long tube, closed at one end, and filling it with this gas ; a test-tube is then filled with a, 

 solutipn of an alkali (for instance, sodium hydroxide), which is then poured into the long 

 tube and the open end is corked. The solution is then well shaken in the tube, and the 

 corked end plunged into water. If the cork be now withdrawn under water, the wate* 

 will fill the tube. The vacuum obtained by the absorption of the carbonic anhydride by 

 an alkali is so complete that even an electric discharge will not pass through it. This 

 method is often applied to produce a vacuum. 



12 The reasons for distinguishing the uni-, bi-, tri-, and quadri-valent metals will be 

 explained hereafter on passing from the univalent metals (Na, K, Li) to the bivalent 

 (Mg. Ca, Ba), Chapter XIV 



