(1) A tap simple of construction, and coating neit to nothing, consists of a cork, having a straight, cleancut hole, through which is inserted a piece of glass tubing sealed at one end, and having a small hole cut on one tide. The position of said hole is determined by the length of cork used. Figs. 330 and 331 show this clearly, where the first shows the tap open; the second shut. The manipulation is done by pressing the tube in and out. Fig. 332 is a jar suitable for photographic or electric cell stock solutions.
Simple forms ol taps.
(2) A different form of tap is shown in Fig. 333. To open and shut the latter form, it is only necessary to turn the tube on its axis, there being a slice cot diagonally off one aide of the cork. This form is specially valuable where it is important that the Tolume of liquid in the containing vessel should remain constant - e. g., burettes (Fig. 334).
It will be observed that the sealed ends of the tubes are slightly inflated; this prevents them being accidentally pulled right out. The hole id easily cut with small, round file, kept wet. The corks may be of cork or rubber, as found most suitable. (K. McLaren).
(3) An indestructible water-tap, invented by Sit William Thomson (Fig. 337), is entirely of metal, no other material being used in its construction. The perishable rubber, fibre, or leather washer-valve employed in ordinary screw-down cock* is entirely dispensed with. The perishable packing or washer generally used around the spindle is also dispensed with. Perfect watertightnesa is, nevertheless, obtained. The metal valve on reaching the seat, also of metal, is not suddenly arrested and compelled to seat itself haphazard, but continues to turn upon its seat as the handle is turned, receiving meanwhile a gradually increasing pressure from a spring, centrally applied th rough the medium of the rounded head of as top. The valve is thus rubbed upon its seat at every opening and closing, and both valve and seat thereby acquire and maintain a perfect lit and burnish. No material wear is shown after the tap has been opened and closed hundreds of thousands of times, and experiments show that even if the seat of the valve be purposely damaged it automatically rights itself. No packing is used to prevent upward leakage.
All water which passes the screw when the tap is open enters an annular space, and is drawn off into the bib through the eduction tube, in which a current is induced by the velocity of the water flowing through the bib. This device is thoroughly effective. The washers used in ordinary cocks are a source of constant trouble and expense. Numerous materials have been tried; but long experience has shown that they differ only in degrees of badness. By Sir William Thomson's invention they are entirely abandoned, and metal to metal is for the first time rendered perfectly water-tight.
Practical men will appreciate the importance of these improvements, whether for cold or hot water. For the first time a screw-down tap has been produced with no perishable parts, and so constructed that the wearing parts - that is to say the valve and its seat - tend rather to improve than deteriorate by use. These taps have now been under test and in use all over the country for more than a year with perfect success, and users may therefore feel assured that in adopting them they are not running any risk or experimenting with an untied invention.
Usually the size of rope is denoted by its circumference in inches. The hemp fibre from which ropes are made is first span into yarn or threads, the longest fibre producing the best rope; several yarns spun together form strands, 3 strands form a hawser laid rope; 3 hawsers or 9 strands form a cable-laid rope, when twisted together. Shroud-laid rope has a central core surrounded by 4 strands. The hawser-laid rope is the one most generally used. The question of the strength of ropes, and their safe working load, under varying circumstances, is of great importance. A series of experiments were carried out in 1873 at the Royal Arsenal, Woolwich, by the Inspector of Machinery, the result of which showed that Italian hemp ropes are stronger than Russian in the proportion of 100 to 79 max. or 93.4 min. Russian hemp ropes are the least rigid in the proportion of Italian 100 to Russian from 80.4 to 96.5, and also that the deterioration of hempen ropes, after a few months wear, although still apparently good, was very marked. With the best rope after 6 months' use, the loss of strength was 25-50 per cent. Thus showing the necessity of allowing a large margin of strength for safety.
Ropes stowed away in damp places, or put away wet, rapidly deteriorate, so that care should be taken to see that the ropes are thoroughly dry before being stored, and that the store-room also is free from damp. If stored away wet, sometimes the rope is worm-eaten in the centre, owing to the development of a species of fungus, probably from the paste used.
The thumb knot a and figure of 8 b (Fig. 338) are used to prevent ropes passing through blocks or slipping. To make the figure of 8 knot, pass the end of the rope under, round, and over the standing part, then up through the bight or loop. The reef knot c is useful for joining together two ropes of equal size. With dry rope, it is equal in strength to the other part. If wet, the knot will generally slip before the rope breaks.