388 CARBONATES. 



ally by the agency of carbonic acid, and appears in the domestic 

 utensils ; it is deposited by boiling, the gas being thus expelled.* 



4. ACTION or PRECEDING BODIES. 



Sa.} Decomposed by acids, with effervescence.-^ 

 b.) No heat is evolved by acids acting on a calcareous carbonate, 

 while with quick lime, there is great heat, especially with sulphuric 

 acid. The same is true of potassa, soda, and magnesia, when com- 

 pared with their carbonates. In the cases in which gas is evolved, 

 the heat is absorbed to form it, and thus becomes latent, and insensi- 

 ble ; the opposite will therefore be true of the caustic substances. 



5. ESTIMATION OF PROPORTIONS. 



(a.) This subject has occupied the attention of many distinguished 

 chemists. The analyses of Dr. Wollaston, Prof. Berzelius, and Dr. 

 Ure coincide so nearly in the proportions of 44 acid and 56 lime, 

 that these numbers have been adopted by Dr. Henry, and they cor- 

 respond with one proportion of acid, 22, and 1 of lime, 28 = 50 for 

 the equivalent. 



(b.) To ascertain the proportion of carbonate of lime in any marl 

 or limestone.^ Effervescence with acids is generally regarded as a 

 proof of the presence of a carbonate of lime. There are, however, 

 carbonates of other substances, and there are other combined gases, 

 besides carbonic acid, that may be disengaged with effervescence, 

 by acids ; but these cases are so rare, and the other so common, 

 that there is little danger of mistake, especially when the peculiar 

 characters of the other carbonates are taken into view. 



(c.) We must not be deceived by the common air lodged in the 

 pores of dry earthy bodies ; when the acid is added, this air is ex- 

 pelled by hydrostatic pressure, and exhibits a false effervescence. 

 The matter should be first immersed in water, and the air thus ex- 

 pelled, and then the acid may be added. 



(d.) For an accurate result, place in one scale, in a flask 100 grs. 

 of the substance, and in a separate vessel, 100 of muriatic acid, mix- 

 ed with 200 of water, and put a counterpoise to the whole in the oppo- 

 site scale. Add the diluted acid, by degrees, till effervescence has 

 ceased, and then weigh the residuum accurately. The loss of weight 

 is the carbonic acid ; therefore, 44 : 100 : : the weight lost to the pro- 

 portion of carbonate of lime, granting that there is no other carbon- 



* The temporarily injurious effects of such waters upon the health of strangers 

 are well known. 



t Even vinegar will, in a degree, produce that effect. 



t See Ure's Diet. 2d Ed. p. 297. 



Carbonate of magnesia may be present. 



From 100 grains of carbonate of lime, 80 or 90 cubic inches of gas arc obtained. It 

 is a rich marl, that has 1-4 of its weight of carbonate of lime, and sometimes marls do 

 not contain more than l-20th. In trying marls, you may reckon 2 1-2 groins of 



