536 
POPULAR SCIENCE REVIEW. 
North Country samples evaporated 9’45 lbs. It is remarkable that whilst 
alone the North Country still appears inferior to the Welsh, the mixture 
of the two has nearly as high an economic value as the pure Welsh, with 
greater rapidity of evaporation, and on the average less smoke. 
Testing of Chain Cables . — An interesting paper on this subject was read 
by Mr. F. A. Paget, C.E., at the Society of Arts. The average tenacity of 
the bars of which the links are made is stated to be 24 tons per square inch ; 
of this 28 # 75 per cent, is lost in the finished link, in consequence of (1) the 
geometrical form of the link, (2) the crushing stress undergone by the 
inside of the crowns, (8) the deterioration of the iron in bending, and (4) 
the loss of strength at the welds. As to the proper tests of the cable, Mr. 
Paget suggests the breaking of a portion by hydraulic pressure as affording 
the surest guide to the quality of the iron employed, testing the entire 
cable to a fixed proof strain, and finally, by blows or impacts, as specially 
adapted for the discovery of false welds. The apparent increase of strength 
of bars repeatedly broken, first exhibited in the experiments of Mr. Lloyd, 
is shown to be due to increase of hardness, or of the difficulty of the gliding 
to and fro of the particles, so that whilst the resistance to purely passive 
loads is increased, the resistance to impulsive forces is enormously 
diminished at each fracture. The value of the Government hydraulic test 
of 11 ’46 tons per square inch is discussed, and the permanent set under 
this strain is stated to be to T l T of the length. While believing that a 
single application of this test does not materially injure the cable if good, 
Mr. Paget deprecates any attempt to make the test more severe. 
Adheated Steam.— Mr. Waterman has patented a plan for making the 
sides of the cylinders of steam engines of extremely thin metal, and sur- 
rounding them by a jacket of steam of higher temperature than that 
working the engine. In this way, the losses from the condensation of 
steam in the cylinder during expansion and its re- evaporation into the 
condenser are avoided. The plan is a thorough carrying out of the 
principle of the ordinary steam jacket, right theoretically, but of doubtful 
practical advantage. 
High pressure Boilers . — Mr. Zerah Colburn has described to the Institute 
of Mechanical Engineers an entirely 
new steam boiler, adapted for very 
high pressures. It is the invention of 
Mr. Joseph Harrison, of Philadelphia, 
and consists of cast-iron spheres con- 
nected by hollow necks and secured by 
bolts. These spheres are 8 in. in ex- 
ternal diam., in. thick and connected 
by necks of 3-in. opening, faced to a 
true surface to secure steam-tight joints. 
Experiments with this boiler in Bel- 
gium, at the request of the Minister of 
Public Works, proved that the boiler 
would not burst with a pressure of 
1,440 lbs. per square inch. Similar ex- 
periments in this country showed that 
the spheres would successfully resist a pressure of 1,200 lbs. Ulti- 
Small portion of a Harrison Boiler. 
Scale ^th. 
