236 Mr. Mallet on the Physical Conditions 



It does not follow that rapid cooling would preclude the escape of such 

 vesicles, if evolved, especially if powerfully aided, as they would be, by centri- 

 fugal force, bringing the7n to the centre and portion of the casting longest fluid, 

 if the whole mould revolved upon its axis, as proposed : in the case of a gun cast 

 solid, depositing such air-vesicles as had not time to escape, in the portion to be 

 bored out; and in the case of one cast on a core, bringing them to the internal 

 surface of the metal in contact therewith, where a ready escape would be found 

 by them. This method of casting would also give great facility to cooling the gun 

 by currents of air through the interior of the core, if found desirable, and admit 

 again of any required slowness of final cooling after consolidation, should 

 such be found to add to tenacity, &c. The author has learned that casting 

 bronze guns in iron flasks, lined with thin coatings of clay, was proposed to the 

 American Ordnance Department ; he is not aware if it was ever tried, or with 

 what results. That proposition, however, is essentially different from the one 

 now made, as the author believes, for the first time, of absolute " chill casting " 

 in naked and massive iron moulds, and with the additions proposed. 



179. Manyexperiments have been made byDussausoy and others, to improve 

 gun-metal by the addition of some other third metal in small proportions. Iron, 

 zinc, lead, antimony, &c., have been tried, in all cases with disadvantageous 

 results. There are metals of one class, however, which have never been tried, 

 and whose addition in minute quantity to gun-metal in the melting furnace 

 would most probably prove a brilliant exception to those failures — namely, the 

 metallic bases of either of the alkalies, potassium or sodium, preferring the 

 latter as most manageable, to be had, even now in commerce, at a moderate 

 price, and capable of being manufactured, were there a demand for it, at a 

 price per ton not much exceeding common zinc. In the author's Third Report 

 on Iron (Trans. Brit. Assoc, for 1843), he has given, some then, new, and 

 remarkable facts, as to the action of sodium, in inducing the alloy, of metals 

 having little affinity, in rendering more perfect and stable the union of all 

 alloys, apparently by rendering the e — and e -1- metals still more electro- 

 negative and positive ; and lastly, in promoting union in metallic alloys, by 

 instantly removing, all traces of suspended or combined oxides from them on 

 its addition, the alkaline metal added, being at once divided into a portion 

 which is decomposed by and reduces the suspended oxide, and another which 



