Mr. T. Andr [Apr. : f ,n. 



tin- cover holding the two plates was then carefully placed closely 

 over a porcelain vessel containing '15 fluid ounces of nitric acid 

 sp. gr. 1'42, the plates being fully immersed in the acid, and the 

 protruding shanks of the bars connected in circuit with the galvano- 

 meter. The electro-chemical effects observed were then taken in the 

 usual manner, and the results are given on Table VIII. 



At the conclusion of each experiment on Table VIII, the nitric 

 acid, though quite colourless at first, was found to be of a yellowish- 

 brown colour. A small deposit of fine black carbonaceous- looking 

 matter was noticed at the bottom of the tank surrounding the 

 wrought-iron bar in each set of these experiments. 



The hard Siemens-Martin steel plate and the wrought-iron plate, 

 instantly after withdrawal from the acid, showed nearly their original 

 bright polish, with the exception of a few fine streaks or markings 

 n the wrought-iron plate, indicating that the latter metal had been 

 rather more acted upon than the steel plate, the hard Siemens-Martin 

 steel plate presenting a slightly dull-greyish aspect. Somewhat 

 similar results were observed on withdrawing the soft cast steel, hard 

 cast steel, soft Bessemer steel, and hard Bessemer steel series of plates 

 from the nitric acid. 



The hard cast steel plate when taken out showed a dull lustre 

 much removed from its original bright polish, but there were no other 

 signs of its having been acted upon. The wrought-iron plate con- 

 nected with it was bright on withdrawal from the liquid and but very 

 slightly marked. 



General Remarks. 



It has been necessary to give in modified detail the effects observed 

 during the periods of experimentation recorded on the Tables, Parts 

 I, II, and III, so as to convey an accurate intimation of the method 

 and nature of the research, and a brief resume of some of the prin- 

 cipal results and conclusions arrived at by the author up to the present 

 time may now be given. 



Firstly. The experimental observations of Part I, Series I, indicate 

 that the influence of magnetisation on the passive state of steel rods 

 in cold nitric acid sp. gr. 1*42 is not very great, but it was detectable 

 with the delicate galvanometer and by the sensitive electro-chemical 

 method pursued by the author in the investigation. 



The effect of magnetisation is more marked in warm nitric acid, 

 and when the iron is in a powdered state, as shown in the independent 

 and separate experiments of Messrs. Nichols and Franklin on passive 

 powdered iron in warm nitric acid, previously alluded to in Part I, 

 by whom it was shown that the temperature of transition from the 

 passive to the active state was very materially lowered by powerful 

 magnetism ; their experiments also indicate that the passive state of 



