METALS. 



501 



being out into appropriate sizes, are heated to 

 redness and cross-rolled into sheets about 29 

 in. square. We quote from the Builder : 



The sheets thus produced are arranged in packets 

 of 3 in each, heated to redness, and rolled, each 

 packet passing through the rolls about 10 times. 

 But, just before rolling, the surface of each packet ia 

 cleaned with a wet broom, usually made of the green 

 leaves of the silver fir, and powdered charcoal is 

 strewn between the sheets. 



The sheets obtained from this rolling are sbeared 

 in the dimensions of 28 in. by 56 in. Each sheared 

 sheet is brushed all over with a mixture of birch- 

 charcoal powder and water and then dried. The 

 sheets, so coated with a thin layer of charcoal-pow- 

 der, are arranged in packets containing from 70 to 

 100 sheets each ; and each packet is bound up in 

 waste sheets, of which 2 are placed at the top and 2 

 at the bottom. A single packet at a time is reheated, 

 with logs of wood about 7 ft. long placed round it, 

 the object of which is to avoid, as far as possible, 

 the presence of free oxygen in the reheating chamber. 

 The gases and vapors evolved from heated wood 

 contain combustible matter, which would tend to 

 protect the sheets from oxidation in the event of free 

 oxygen finding its way into the reheating chamber. 

 The packet is heated slowly during 5 or 6 hours, 

 after which it is taken out by means of large tongs 

 and hammered. 



The actual cost of manufacturing these Eussian 

 Bheets is about 12 15s. per ton, to which must be 

 added general charges, which raise the amount to 

 16 or 17 per ton, exclusive of profit. The average 

 price of sheet-iron at the fair of Nijni-Novgorod is 

 about 22 or 25 per ton. 



Iron Paper. The iron manufacturers of 

 Europe and America have competed to see 

 who could make the thinnest iron paper. It 

 had been rolled down to various degrees of 

 tenuity, ranging from 1,000 to 3,797 sheets to 

 the inch; but now comes a claim from the 

 Upper Forest Tin-Works near Swansea, which 

 seems to throw all others into the shade. The 

 Mining Journal reports that the iron from 

 which the sheet was rolled was made on 

 the premises. It was worked in a finery 

 with charcoal and the usual blast; afterward 

 taken to the hammer, to be formed into a 

 regular flat-bottom; thence conveyed to the 

 balling-furnace, and when sufficiently heated 

 taken to the rolls, lengthened, and cut by 

 shears into proper lengths, piled up, and trans- 

 ferred to the balling-furnace again; when 

 heated it was passed through the rolls, hack 

 again into the hailing- furnace, and when duly 

 brought to the proper pitch was taken to the 

 rolls, and made into a thoroughly good bar. 

 Such is the history in connection with the forge 

 department. It was then taken to the tin- 

 mills, and rolled till it was supposed to he thin- 

 ner than 23 grains, afterward passed through 

 the cold rolls to give it the necessary polish, 

 and now it stands on record as the thinnest 

 sheet of iron ever rolled. The sheet in ques- 

 tion is 10 in. by 5 in., or 55 in. in surface, 

 and weighs but 20 grains, which, being brought 

 to the standard of 8 in. by 5-J in., or 44 surface 

 inches, is but 16 grains, or 30 per cent, less 

 than any previous effort, and requires at least 

 4,800 to make 1 in. in thickness. 



Effects of Cold on Iron. Mr. P. Spence, as 



reported in the Mining Journal, has made a 

 new set of experiments to determine the effects 

 of cold on iron, limiting himself to the inquiry 

 whether the reduction of temperature had any 

 effect on cast-iron with regard to its powers 

 of resisting transverse strain either of weight 

 or pressure. He experimented on the ordinary 

 iron in the market, cast into 50 bars 3 feet 

 long and \ in. square : 



Mr. Spence cut each bar into three lengtbs of 1 ft., 

 the 150 pieces being thrown together in a heap; 

 the ends were then covered with paint, that the new 

 fracture might be examined ; and the heap was then 

 taken into his laboratory, so that it had three cbances 

 of perfect mixing. A boy eleven years old now- 

 handed him the pieces singly from the heap, and he 

 placed them alternately one by one in two lots, until 

 he had got 75 pieces in each lot. One lot was placed 

 in a freezing mixture, standing at zero, for nearly 48 

 hours, and the other lot was put into water at 70 

 Fabr., chiefly that the pieces might be broken wet, 

 as those would necessarily be when taken out of the 

 freezing mixture. The distance between the sup- 

 ports was exactly 9 in. in every case; and Mr. 

 Spence' s experiments prove that "cast-iron, having 

 at 70 Fahr. a given power of resistance to trans- 

 verse strain, will, on its temperature being reduced 

 to zero, have that power increased by 3 per cent." 

 At the temperature of 70 Fahr., the maximum 

 breaking weight was 4 cwt. 3 qrs. 26 Ibs., and the 

 minimum 2 cwt. 2 qrs. 14 Ibs., equal to an average 

 of 3 cwt. 3 qrs. 6 Ibs. At zero, the maximum break- 

 ing weight was 4 cwt. 3 qrs. 13 Ibs., and the mini- 

 mum 2 cwt. 3 qrs. 10 Ibs., equal to an average 

 of 3 cwt. 3 qrs. 11 Ibs. The difference, therefore, 

 is but 5 Ibs., or less than 12 per cent, increase, by 

 the reduction of temperature. Adding together, 

 however, the breaking weights of the 70 samples 

 tested at 70 Fahr., the total is 268 cwt. 3 qrs. 18 Ibs., 

 equal to an average of 3 cwt. 3 qrs. 10i Ibs. The 

 total breaking weight of the 70 samples tested at 

 zero was 276 cwt. 3 qrs., equal to an average of 3 cwt. 

 3 qrs. 22* Ibs. The difference thus shown is 12i Ibs., 

 or about 3 per cent, increase, as Mr. Spence states. 



Action of Water on Iron. M. Sainte-Claire 

 Deville has fully investigated this subject, tak- 

 ing perfectly pure iron for his experiments, 

 and exposing it to the action of water-vapor 

 of known tension and temperature, at the 

 same time maintaining a constant temperature 

 of the iron. His apparatus was a porcelain 

 tube, which contained the iron and communi- 

 cated at one end with a glass retort which 

 furnished the water- vapor, and at the other 

 end with a manometer. He found, says the 

 Mining Journal: 1. That iron continues to 

 oxidize in water-vapor, until at a fixed tem- 

 perature the tension of the hydrogen set free 

 becomes constant. 2. At the point of maxi- 

 mum tension for any given temperature, less- 

 ening the pressure, hy withdrawal of some of 

 the hydrogen, causes a renewal of the action 

 of the iron on the vapor, which continues till 

 the constant is restored ; or if hydrogen is sent 

 into the apparatus, so that the pressure is in- 

 creased beyond the constant value, some oxide 

 of iron is reduced, and the pressure restored 

 hy the condensation of the water thus formed. 



3. When heat is applied to the apparatus, the 

 tension is preserved by the condensation of 

 some of the hydrogen on the oxide of iron. 



4. When the temperature of the vapor is main- 



