252 
POPULAR SCIENCE REVIEW. 
lead, rich in silver, is run off from the bottom. Strong iron hooks are inserted 
in the mass of lead and coke before complete solidification takes place, and 
the mass is lifted from the pan by a crane. The pan is then ready for a 
second operation. — See also Chemical News. 
Crushing Masses of Cast Iron.- — The ordinary methods of crushing large 
masses of cast iron into fragments are both cumbersome and expensive, but 
by the means which has lately been described in Les Monies, this operation 
may be conducted with considerable ease. The new French method consists 
in drilling a hole in the mass of cast iron, for about one-third of its thickness, 
filling this with water, closing it with a steel plug which fits accurately, and 
letting the ram of a pile-driver fall on the plug. The very first blow splits 
up the mass. 
Native Borax. — A lake about two miles in circumference, from which borax 
is obtained in extremely pure condition and in very large quantity, has 
recently been discovered in California. The borax hitherto in use has been 
procured by combining boracic acid, procured from Tuscany, with soda. It 
is used in large quantities in this country, the potteries of Staffordshire 
alone consuming more than 1,100 tons annually. 
Obtaining Soda from Cryolite. — The Salt and Alkali Manufacturing 
Company of Pennsylvania are at present trying a process of obtaining soda, 
which consists in mixing cryolite with lime and heating it. The fluorine 
leaves the cryolite and combines with the calcium of the lime, forming fluoride 
of calcium, while the two metals remaining absorb oxygen, becoming alumina 
and soda — a soluble compound. This is treated with carbonic acid, which 
combines with the soda, forming carbonate of soda ; this remains in solution, 
while the alumina, being insoluble, is precipitated. Carbonate of soda once 
obtained is treated in the usual way. 
IIow to protect Iron from Oxidation. — In some of our late numbers we 
spoke of the extreme degree of tenuity to which iron plates can now be 
brought. A curious property of these plates has recently been observed : they 
resist oxidation in an extraordinary degree. There is no doubt but that this 
is attributable to a fused layer of magnetic oxide, with which they are always 
covered ; and the fact has been applied to the protection of articles of wrought 
iron. The latter are embedded in a pulverized layer of native oxide of iron — 
hsematite, for instance — and kept at a full red heat for several hours, after 
which they are allowed to cool gradually. Plates treated in this way are 
perfectly covered with the oxide, and are well suited for shipbuilding. A 
combination of the oxides of zinc and iron, formed by the use of oxide of zinc 
also in the process, gives rise to a black coating, which is, perhaps, even 
more effective. — See the Scientific Bevieiv, March. 
English Petroleum. — It is found that mineral oil can be produced at the 
cost of sixpence per gallon from the shales of unctuous clay overlying the 
ironstone deposits of the moors in the North Biding of Yorkshire. This 
circumstance is of much importance, and promises to effect a good deal for 
the industry of the district in which the petroleum shale occurs. 
Progress of the Mont Cenis Tunnel. — According ’to the assurances of the 
contractors, the international railway between France and Italy via the Alps 
will be open for passengers at the latest in 1871, unless some unforeseen 
accident should mar the progress of the present operations. The Gazctta di 
