Welds made with steam hammer were 10 per cent, stronger for mild steel and 5 per cent, stronger for wrought iron on the average than hand welds.

Results Of Tests By W. C. Unwin1

Percentage of Carbon

Ratio of strength at weld to strength of bar, per cent.

Series A

Series B

o.75

59

68

1.OO

76

51

1.00

50

84

1-15

89

113

1.15

75

117

1.25

75

86

RESULTS OF TESTS BY DAVID KIRKALDY & SON2

Kind

No.

of tests

Size of test bar, inches

Ratio of strength at weld to strength of bar, per cent.

Mean

Range

17

1.129 diam.

89.1

19

1.116 diam.

89.3

Steel bolts, welded. .

28

7/8 to 2½ diam.

75.1

71.5 to 88.8

Iron bolts, welded. . .

181

½ to 2½ diam.

73.8

61.7 to 88.2

Iron tie-bars, welded.

18

1½ to 3.13 diam.

59

37 to 74.2

Iron tie-bars, welded.

10

2.5 x (.24 to 68)

76.7

Iron plates, welded . .

7.

10 x.87 to 6x 1.11

65.5

57.7 to 83.9

1086

1/10 to 2 (area turned)

86.4

72.1 to 95.4

Bar plate, welded. . .

14

½ to 1 1/8 thickness

68.8

52.6 to 82.1

1 "Testing of Materials of Construction," 1899.

2 "Strength and Properties of Materials," W. G. Kirkaldy, 1891.

Conclusions. - Holley1 gives three conclusions concerning iron:

" 1. None of the ingredients except carbon in the proportions present seems very notably to affect the welding by ordinary methods.

"2. The welding power by ordinary methods is varied as much by the amount of reduction in rolling as by the ordinary differences in composition.

"3. The ordinary practice of welding is capable of radical improvement, the most promising field being in the direction of welding in a non-oxidizing atmosphere."

He gives his maximums for the impurities as follows: P, 0.317; S, 0.015; Si, 0.321; Mn, 0.097; Cu, 0.45; Ni, 0.34; Co, o. 11; slag, 2.262.

Campbell's deductions are:

"1. With the exception of manganese in small proportion, the usual impurities in steel reduce its welding power by lowering the critical temperature at which it becomes coarsely crystalline.

"2. A small content of manganese aids welding by preventing crystallization.

"3. Only the purest and softest steels can be welded with any reasonable assurance of success.

" 4. The confidence of a smith in his own powers and his belief in the perfection of the weld is no guarantee that the bar is fit to use."

According to Kent:2 "No welding should be allowed on any steel that enters into structures."