COMPOUNDS ol' MTI{()(iKN WITH HYDROGEN AM) OXYGEN 28B 



a definite quantity, then a definite quantity of sulphuric acid and nitric 

 oxide will be formed, according to the preceding equation ; but there 

 the reaction ends, the excess of sulphurous anhydride, if there be any, 

 will remain unchanged. But if we add air and water, then the nitric 

 oxide will unite with the oxygen to form nitrogen peroxide, and the 

 latter with water to form nitric and nitrous acids, which again give 

 sulphuric acid from a fresh quantity of sulphurous anhydride. Nitric 

 oxide is again formed, which is able to start the oxidation afresh if 

 there be sufficient air. Thus it is possible with a definite quantity of 

 nitric oxide to convert an indefinitely large quantity of sulphurous 

 anhydride into sulphuric acid, water and oxygen only being required. 64 

 This may be easily demonstrated by an experiment on a small scale, if 

 a certain quantity of nitric oxide be first introduced into a flask, and 

 sulphurous anhydride, steam, and oxygen be then continually passed in. 

 Thus the above-described reaction may be expressed in the following 

 manner : 



if we consider only the original substances and those finally formed. 

 Thus a definite quantity of nitric oxide may serve for the conversion of 

 an indefinite quantity of 'sulphurous anhydride, oxygen, and water into 

 sulphuric acid. In reality, however, there is a limit to this, because a 

 portion of the resulting oxides of nitrogen are dissolved by the sulphuric 

 acid, so that in employing even pure oxygen the amount of free (undis- 

 solved) or active nitric oxide decreases little by little. If air, and not 

 pure oxygen, be employed for the oxidation, as it is necessary to do in 

 practice, then it is necessary to remove the nitrogen of the air and to 

 introduce a fresh quantity of air. A certain quantity of nitric oxide 

 will pass away with this nitrogen, and will in this way be lost. 65 



64 The instance of the action of a small quantity of NO in inciting a definite 

 chemical reaction between large masses (SOo + O + H.>O = H. 2 SO 4 ) is very instructive, 

 because the particulars relating to it have been studied, and show that intermediate 

 forms of reaction may be discovered in the so-called contact or catalytic phenomena. 

 The essence of the matter here is that A ( = SO.>) reacts upon B ( = O and H 2 O) in the pre- 

 sence of C, because it gives BC, a substance which forms AB with A, and again liberates 

 C. Consequently C is a medium, a transferring substance, without which the matter does 

 not proceed of its own accord. Many similar phenomena may be found in other depart- 

 ments of life. Thus the merchant is an indispensable medium between the producer and 

 the consumer ; thus experiment is a medium between the phenomena of nature and the 

 cognisant faculties; thus Umi:uiige, forms, and laws are media which are as necessary 

 for the consolidation i.f social intercourse as nitric oxide for the relations between sul- 

 phurous anhydride and oxygen and water. 



65 If the sulphurous anhydride be prepared by roasting iron pyrites, FeS.,>, then 

 each equivalent of pyrites (equivalent of iron 56, of sulphur 82, of pyrites 120) requires 

 .six equivalents of oxygen (that is 96 parts) for the conversion of its sulphur into sul- 



