RADICALS AND ACIDS. 4 1 I 



The importance of these facts to science is unmistakable, and, indeed, 

 many attempts have been made to explain, from the electrical condition of 

 the elements, the nature of chemical affinity, and of chemical phenomena in 

 general. 



Electrotyping is another instance of decomposition by means of electricity, 

 and respecting decomposition by light we know how powerful the action of 

 the sun's rays are upon plants, and for the evolution of oxygen. The 

 daguerreotype and photographic processes are also instances which we have 

 commented upon. So we can pass directly to the consideration of the 

 compound groups. 



In nearly every complex organic compound we have a relatively simple 

 one of great stability, which is termed the radical, which forms, with other 

 bodies, a compound radical.* In these complex groups we find certain 

 elements generally, viz., carbon, hydrogen, nitrogen, sulphur, and phosphorus. 

 Some compounds may consist of two of these, but the majority contain 

 three (hydrogen, oxygen, and carbon). Many have four (carbon, oxygen, 

 hydrogen, and nitrogen), and some more than four, including phosphorus 

 and sulphur. Others, again, may contain chlorine and its relatives, arsenic, 

 etc., in addition. Now we will all admit that in any case in which carbon 

 is present in composition with other simple bodies forming an organic body, 

 and if that body be ignited in the air, it burns and leaves (generally) a black 

 mass. This is a sure test of the presence of carbon, and forms an organic 

 compound. Similarly in decomposition nitrogen and sulphur in combination 

 inform us they are present by the odour they give off. We need not go 

 farther into this question of radicals and compound radicals than to state 

 that a compound radical plays the part of an element in combination. We 

 find in alcohol and ether a certain combination termed Ethyl. This 

 "compound radical" occurs in same proportions in ether, chloride of ethyl, 

 iodide of ethyl, etc., as C 2 H 5 ; so it really acts as a simple body or element, 

 though it is a compound of carbon and hydrogen. A simple radical is easily 

 understood ; it is an element, like potassium, for instance. We may 

 now pass to the organic combinations classified into ACIDS, BASES, and 

 INDIFFERENT, or NEUTRAL, BODIES. 



I. ACIDS. 



There are several well-known organic acids, which we find in fruits and 

 in plants. They are volatile and non-volatile ; acids are sometimes known 

 as " Salts of Hydrogen." We have a number of acids whose names are 

 familiar to us, viz., acetic, tartaric, citric, malic, oxalic, tannic, formic, lactic, 

 etc. 



Acetic acid (HC 2 H 4 O 2 ) is a very important one, and is easily found 

 when vegetable juices, which ferment, are exposed to the air, or when wood 

 and other vegetable matter is subjected to the process of " dry distillation." 



* Cyanogen, ethyl, and cacodyl, are compound radicals. 



