384 Progress of Invention. 



In mottled cast iron, the ferrosum and ferricum retain their peculiari- 

 ties ; the white portions being formed by ferrosum in combination 

 •with carbon, and the dark by ferricum with its deposit of carbon. 

 White crystallized cast iron consists of ferrosum in combination with 

 carbon. Ferrosum is characterised by being obtained at very low 

 temperature, and, when combined with carbon, is hard and brittle. 

 The characteristics of ferricum are its abandonment of carbon, 

 during slow cooling, and its malleability. It cannot by itself form 

 stable steel ; it requires for this purpose to be mixed with fer- 

 rosum, which passes into the state of ferricum without losing its 

 hardness. Ferricum, unless it has been originally ferrosum, can- 

 not be changed to it. The nature of the re-agents, and the 

 degree of temperature used in the production of iron, modify the 

 proportions of ferrosum and ferricum in the result. Thus oxide of 

 carbon, which contains only one atom of oxygen, favours the pro- 

 duction of ferrosum ; bodies which, like phosphorus, combine with 

 some uneven number of atoms of oxygen, not less than three, favour 

 the production of ferricum. A low temperature tends to produce 

 ferrosum, a high one ferricum. To obtain the best commercial iron, 

 the nature of the ore, the re-agents, and the temperature must all 

 harmonize. The employment of suitable re-agents shortens the 

 time during which it is necessary to employ a given temperature, in 

 order to obtain a certain kind of iron. The sudden coolinar of steel 

 causes carbon, which slow cooling would separate, to be retained in 

 combination — with the ferrosum permanently, with the ferricum in 

 such a way that subsequent tempering liberates it, and restores 

 malleability. If the relative proportions of ferrosum and ferricum 

 depend on the temperature and re-agents which have been employed 

 in the manufacture, and not on the ore which has been used, they 

 will be more or less unstable ; and the quality of the iron will be im- 

 paired — slowly by time, and rapidly by repeated vibrations ; which 

 explains many causes of the breakage of axles, etc. There is reason 

 to suppose that the calorific capacity of iron depends on the relative 

 amounts of the ferrosum and ferricum which it contains ; should such 

 prove to be the case, calorific capacity may afford a simple and 

 reliable test of the quality of iron. 



New Galvanic Battery. — It has been found that a battery, the 

 elements of which are silver and magnesium, is far more powerful 

 than one of equal size consisting of copper and zinc. M. Bultinck 

 found that when silver and magnesium, immersed in pure water, 

 caused the galvanometer to be deflected temporally 90°, and perma- 

 nently 28°, copper and zinc, in the same circumstances, caused a 

 temporary deflection of only 30", and a permanent one of only 10°. 

 And when silver and magnesium were used, the same result was 

 obtained with pure water, as when a dilute acid or saline solution 

 was employed with copper and zinc. 



Graphitic Acid. — This curious compound, which was discovered 

 by Sir B. Brodie, has been recently examiued by Dr. Gottschalk, 

 who has discovered its constitution to be G 2S He O,.. It is formed 

 by heating pure graphite several times in succession with chlorate 

 of potash, and the strongest nitric acid. The colour of the graphite 



