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On The Testing And Strength Of Railway Materials, &C.
weights , and that no strain shall be applied in any AA'ay by test levers ; and , in important contracts , bars must be cast in duplicate , one to test ancl the other marked Avith the date AA'hen run , and kept for future reference by the engineer . The area of the flanges of cast iron girders should , theoretically , be in the proportion of six or seven to one ; but the upper flange , AA'here the girder is isolated ancl not held in position by the structure itself , should be proportionally wider according to each particular case as it has to resist flexurewhich Avould possibly deform it before compression of the flange could occur ;
, but , AA'here the Aveb ancl the upper flange are supported by the structure itself , as in the cases of arches ancl flooring , the aboA'e proportion may be taken . As a a general rule Ave may , in designing cast iron girders , make the depth from one-twelfth to one-sixteenth of span ; bottom flange , from two-thirds to three-fourths the depth in centre ; top flange , one-third to one-half the AA'idth of bottom ; maximum span , Soft . ; over this span , wrought iron becomes as economical and safer . I believe ( says the author ) some of our
members are of tho opinion that strengthening Avebs , sometimes called gussets or ribs , should not be cast on girders , as the metal is clraAvn away from the flanges in cooling ; others that at the junction of Aveb and flange , the rib , if broken away , will frequently be found honey-combed . In a paper read by the late Zerah Colbuni , before the Society of Engineers , April 3 , 1865 , he describes the American practice of re-melting all the iron employed for cannon , ancl keeping it for some time in fusion . This practice at one time went so far as three and eA'en four re-meltings—the iron being kept in the fluid
state for three hours at each melting . In this AA'ay the tensile strength of iron , ranging from 5 to 6 £ tons in the pig , has become !) tons at the first casting ; ancl , after remaining in the melted state for tAvo hours , 13 tons at the second casting ; and 15 £ . tons per square inch at the third casting , the period of fusion at each melting being from one to three hours . Castings overstrained in cooling are apt to break under even a moderate degree of vibration ; thus , Hodgkinson ' s formula of six to one in the flanges of cast girders , are scarcely , if ever , carried out in practice ; as , with these proportions , the casting AA'ould , in all probability , crack in cooling . Castings should cool equally in such a manner as not to leave them subject to considerable internal strains .
PORTLAND CEMENT .
Mr . H . Reid , C . E ., in his " Science ancl Art of Portland Cement , ' sums up the points Avhich indicate the quality of this material as folloAvs : — 1 st . That the clinker of the true quality should be a dark greenish mass , homogenous and slightly A'itrified . 2 nd . A clinker of metallic hardness , Avith a black lustre , is the result of an excess of carbonate of lime , caused by Avasteful application of fuel , ancl its cost of grinding
is high . 3 rd . The true normal clinker exhibits , when drawn from the kiln , a rough , lava-like texture , haying a tinge of green or bronze glitter Avhen exposed to light . Generally , the conclusions are : 1 st , that a clinker of a brown colour , dusting freely , indicates an abnormal or dangerous cement , and Aveak in indurating power ; 2 nd , the blackish clinker , producing a bluish-grey poAvder , is unfit for use until matured
by exposure ; 3 rd , the true clinker of greenish tinge , of light grey powder , can be used at once . Experiments have proved , also , that the constructive value of cement when mixed with sand emends on its being finely ground . LIVERPOOL COPOBATION TEST . 1 st . Samples of the cement being sifted through a No . 50 gauge wire sievemust
, not leave a residue of more than 10 per cent . 2 nd . Samples of pure cement Avill be gauged AA'ith water , and placed in the brass moulds used by the Corporation within twenty-four hours ; the casts thus made will be immersed in still water , in Avhich they will remain until the expiration of the seven days from the date of moulding , AA'hen they Avill be taken out of the water and tested
Note: This text has been automatically extracted via Optical Character Recognition (OCR) software.
On The Testing And Strength Of Railway Materials, &C.
weights , and that no strain shall be applied in any AA'ay by test levers ; and , in important contracts , bars must be cast in duplicate , one to test ancl the other marked Avith the date AA'hen run , and kept for future reference by the engineer . The area of the flanges of cast iron girders should , theoretically , be in the proportion of six or seven to one ; but the upper flange , AA'here the girder is isolated ancl not held in position by the structure itself , should be proportionally wider according to each particular case as it has to resist flexurewhich Avould possibly deform it before compression of the flange could occur ;
, but , AA'here the Aveb ancl the upper flange are supported by the structure itself , as in the cases of arches ancl flooring , the aboA'e proportion may be taken . As a a general rule Ave may , in designing cast iron girders , make the depth from one-twelfth to one-sixteenth of span ; bottom flange , from two-thirds to three-fourths the depth in centre ; top flange , one-third to one-half the AA'idth of bottom ; maximum span , Soft . ; over this span , wrought iron becomes as economical and safer . I believe ( says the author ) some of our
members are of tho opinion that strengthening Avebs , sometimes called gussets or ribs , should not be cast on girders , as the metal is clraAvn away from the flanges in cooling ; others that at the junction of Aveb and flange , the rib , if broken away , will frequently be found honey-combed . In a paper read by the late Zerah Colbuni , before the Society of Engineers , April 3 , 1865 , he describes the American practice of re-melting all the iron employed for cannon , ancl keeping it for some time in fusion . This practice at one time went so far as three and eA'en four re-meltings—the iron being kept in the fluid
state for three hours at each melting . In this AA'ay the tensile strength of iron , ranging from 5 to 6 £ tons in the pig , has become !) tons at the first casting ; ancl , after remaining in the melted state for tAvo hours , 13 tons at the second casting ; and 15 £ . tons per square inch at the third casting , the period of fusion at each melting being from one to three hours . Castings overstrained in cooling are apt to break under even a moderate degree of vibration ; thus , Hodgkinson ' s formula of six to one in the flanges of cast girders , are scarcely , if ever , carried out in practice ; as , with these proportions , the casting AA'ould , in all probability , crack in cooling . Castings should cool equally in such a manner as not to leave them subject to considerable internal strains .
PORTLAND CEMENT .
Mr . H . Reid , C . E ., in his " Science ancl Art of Portland Cement , ' sums up the points Avhich indicate the quality of this material as folloAvs : — 1 st . That the clinker of the true quality should be a dark greenish mass , homogenous and slightly A'itrified . 2 nd . A clinker of metallic hardness , Avith a black lustre , is the result of an excess of carbonate of lime , caused by Avasteful application of fuel , ancl its cost of grinding
is high . 3 rd . The true normal clinker exhibits , when drawn from the kiln , a rough , lava-like texture , haying a tinge of green or bronze glitter Avhen exposed to light . Generally , the conclusions are : 1 st , that a clinker of a brown colour , dusting freely , indicates an abnormal or dangerous cement , and Aveak in indurating power ; 2 nd , the blackish clinker , producing a bluish-grey poAvder , is unfit for use until matured
by exposure ; 3 rd , the true clinker of greenish tinge , of light grey powder , can be used at once . Experiments have proved , also , that the constructive value of cement when mixed with sand emends on its being finely ground . LIVERPOOL COPOBATION TEST . 1 st . Samples of the cement being sifted through a No . 50 gauge wire sievemust
, not leave a residue of more than 10 per cent . 2 nd . Samples of pure cement Avill be gauged AA'ith water , and placed in the brass moulds used by the Corporation within twenty-four hours ; the casts thus made will be immersed in still water , in Avhich they will remain until the expiration of the seven days from the date of moulding , AA'hen they Avill be taken out of the water and tested