Part 8 (1/2)

Ceer to harden than ifin proportion to the aravel froh dry, have their surfaces covered with salineof the cement, even when fresh water is used, as they become mixed with such water, and thus perate from the shore are used, care anic matter is mixed with it, as every such piece will cause a weak place in the concrete If loam, clay, or other earthy matters frole must be washed before it is used in concrete

Exposure to damp air, such as is unavoidable on the coast, considerably retards the setting of cement, so that it is desirable that it should not be further retarded by the addition of gypsum, or calcium sulphate, especially if it is to be used with sea water or sea-washed sand and gravel The percentage of gypsuenerally considerably below the maximum allowed by the British Standard Specification, viz, 2 per cent, and is so small that, for practical purposes, it h of course, within reasonable limits, the quicker the cement sets the better When cement is used to joint stoneware pipe sewers near the coast, allowance , and any internal water tests which er period has elapsed after the laying of the pipes than would otherwise be necessary A high proportion of aluration when exposed to sea water The ood sound cement after exposure to the sea is an increase in the chlorides, while a slight increase in the nesia and the sulphates also takes place, so that the proportion of sulphates and nesia in the cement should be kept fairly low Hydraulic linesia and sulphates

To summarise the information upon this point, it appears that it is better to use fresh water for all purposes, but if, for the sake of economy, salinesea water for le from the beach, the principal effect will be to delay the tith of the concrete will probably not be seriously affected When the concrete is placed in position the portion h and loater mark, which is alternately exposed to the action of the sea and the air, but if the concrete has a well-graded aggregate, is densely mixed, and contains not more than two parts of sand to one part of cement, no ill-effect need be anticipated

CHAPTER XII

DIVING

The engineer is not directly concerned with the variousa sea outfall, suchleft to the discretion of the contractor It may, however, be briefly stated that the work frequently involves the erection of tened and solidly built if they are to escape destruction by the heavy seas It is ah sea will twist into er in size Any extra cost incurred in strengthening the gantries is well repaid if it avoids dae, because otherwise there is not only the expense of rebuilding the structure to be faced, but the construction of the ill be delayed possibly into another season

In order to ensure that the works beloater are constructed in a substantial ineer, at least, should be able to don a diving dress and inspect the work personally The particular points to which attentionof the pipes, so that the spigot of one is forced ho up of all the bolts required to be fixed, the proper driving of the piles and fixing the bracing, the dredging of a clear space in the bed of the sea in front of the outlet pipe, and other matters dependent upon the special for is inserted in the open end of the pipes as laid, the rising of the tide will press on the plugged end and be of considerable assistance in pushi+ng the pipes home; it will therefore be necessary to re-exahtened up any more

Messrs Siebe, Gorman, and Co, the well-known makers of submarine appliances, have fitted up at their works at Weste-road, London, SE, an experiineers may make a few preli; and it is distinctly e in this way frouidance of the divers engaged upon the hich the engineer desires to inspect Only a nouinea for two descents is made, which sum, less out-of-pocket expenses, is remitted to the Benevolent Fund of the Institution of Civil Engineers It is generally desirable that a co the air puineer, and specialand to attend to his wants while he is beloater He is then able to inspect the hile it is actually in progress, and he will not hinder or delay the divers

It is a wise precaution to be h, with the short tienerally be spent beloater, and the shallow depths usual in this class of work, there is practically no danger; but, generally speaking, a diver should be of good physique, not unduly stout, free fro trouble and varicose veins, and should not drink or smoke to excess It is necessary, however, to have acquaintance with the physical principles involved, and to knohat to do in eiven by Mr R H

Davis in his ”Diving Manual” (Siebe, Gor notes are taken

A diving dress and equipht carried by the diver on his chest, a siht on his back, and l6lb of lead on each boot Upon entering the water the superfluous air in the dress is driven out through the outlet valve in the hels and body, and by the time the top of the diver's head reaches the surface his breathing becos equals the atmospheric pressure, while the pressure upon his chest and abdoht of the water thereon

He is thus breathing against a pressure, and if he has to breathe deeply, as during exertion, the effect beco he has to learn is to adjust the pressure of the spring on the outlet valve, so that the amount of air pu dress counterbalances the pressure of the water outside, which is equal to a little under 1/2lb per square inch for every foot in depth If the diver be 6 ft tall, and stands in an upright position, the pressure on his helmet will be about 3lb per square inch less than on his boots The breathing is easier if the dress is kept inflated down to the abdo capsized and floating feet upwards, in which position he is helpless, and the air cannot escape by the outlet valve Air is supplied to the diver under pressure by an air puht rope called a life line, which is used for signalling, connects the man with the surface The descent isabout 50 lb attached, and is previously lowered to the botto, called a ”distance- line,” is attached to the shot-rope about 3 ft above the sinker, and on reaching the bottom the diver takes this line with him to enable him to find his way back to the shot-rope, and thus reach the surface co hauled up by his life line The diver must be careful in his movements that he does not fall so as suddenly to increase the depth of water in which he is iher level the air pressure in the dress will be properly balanced against the water pressure; but if he falls, say 30 ft, the pressure of the water on his body will be increased by about 15 lb per square inch, and as the air pump cannot immediately increase the pressure in the dress to a corresponding extent, thedress will be forced into the rigid helmet, and he will certainly be severely injured, and perhaps even killed

When descending under water the air pressure in the dress is increased, and acts upon the outside of the druh the nose and up the Eustachian tube inside the head reaches the back of the drum and balances the pressure This may be delayed, or prevented, if the tube is partially stopped up by reason of a cold or other cause, but the balance can generally be brought about if the diver pauses in his descent and ss his saliva; or blocks up his nose as ainst the front of the hel effort at expiration so as to produce temporarily an extra pressure inside the throat, and so blow open the tubes; or by yawning or going through the ain Provided his ears are ”open,” and the air pumps can keep the pressure of air equal to that of the depth of the water in which the diverto li, carbonic acid gas is exhaled, the quality varying in accordance with the amount of work done, from 014 cubic feet per as must be removed by dilution with fresh air so as not to inconvenience the diver This is not a matter of much difficulty as the proportion in fresh air is about 03 per cent, and no effect is felt until the proportion is increased to about 03 per cent, which causes one to breathe twice as deeply as usual; at 06 per cent there is severe panting; and at a little over 10 per cent unconsciousness occurs The effect of the carbonic acid on the diver, however, increases the deeper he descends; and at a depth of 33 ft 1 per cent of carbonic acid will have the same effect as 2 per cent at the surface If the diver feels bad while under water he should signal forabout, and rest quietly for a minute or then the fresh air will revive him The volume of air required by the diver for respiration is about 15 cubic feet per minute, and there is a non-return valve on the air inlet, so that in the event of the air pipe being broken, or the pu the outlet valve the diver could retain sufficient air to enable hi the tias from the air is absorbed by his blood and the tissues of his body This does not inconvenience hiiven off, so that if he has been at a great depth for some considerable time, and coht side of the heart with air, causing death in a few minutes In less sudden cases the bubbles fors, which is called divers' palsy, or the only trouble which is experienced may be severe pains in the joints and muscles It is necessary, therefore, that he shall coradually and avoid danger

The blood can hold about twice as as in solution as an equal quantity of water, and when the diver is working in shallow depths, up to, say, 30 ft, the aen absorbed is so s as is necessary for the purposes of the work, and can coer At greater depths approximately the first half of the upward journey rees, the longest rest beingtable shows the time limits in accordance with the latest British Ad that fro of the ascent:--

TABLE No l7--DIVING DATA

Stoppages in Total time minutes at for ascent Depth in feet Time under water different depths in minutes

at 20 ft 10 ft

Up to 36 No limit - - 0 to 1

36 to 42 Up to 3 hours - - 1 to 1-1/2 Over 3 hours - 5 6

42 to 48 Up to 1 hour - - 1-1/2 1 to 3 hours - 5 6-1/2 Over 3 hours - 10 11-1/2

48 to 54 Up to 1/2 hour - - 2 1/2 to 1-1/2 hour - 5 7 1-1/2 to 3 hours - 10 12 Over 3 hours - 20 22