cotton, very little more than 20 per cent. in single yarns of the theoretical strength of the fibres is utilized. In two-fold yarns a better result by about 6 per cent. is obtained. The percentage of loss increases in both cases as the yarns become finer. In making these tests yarns were in all cases used, spun down from the highest counts in order to obtain them from the same cotton: that is to say, the American single yarns were spun down from 50s rovings, and the Egyptian singles from 60 rovings; and similarly in the two-folds, all the Egyptians being from the same rovings and cotton as the 90s/2. The result shows that there is room for further improvement.

Twist for doubling of yarns.-Yarns after their first spinning are often twisted together again in two, three, four and many other folds for various requirements. This process is technically called "doubling," a name which it is obvious only very imperfectly describes it. Several strands thus produced from two or more threads are frequently again put together, making a cord of any number of threads according to requirement. The amount of twist or twine to put into the article at the respective doublings is often a difficulty to those having charge of the operations, especially as practical men differ about the matter. The consequence is, that yarn is sometimes spoiled in the endeavour to feel the way to a proper result. The best practice is to follow the principle laid down for obtaining the twist in spinning single yarns. Yarns doubled on that principle will lie straight as in the single state. Suppose 100s has to be doubled into two-fold; two threads of 100s put together, the joint thread would be 50s, the square root of this number is 7.05, which multiplied by 33, or thus, 3.75 gives 26.43 for twist. If the doubled yarn be wanted of a soft texture, then the square root as obtained above should be multiplied by 34, when the twist will be such as will set without curl. When curl is required, an additional percentage to the above twist must be put in. In all cases the twist should be put in in the direction

opposite to that of the last preceding process. Suppose now three strands of this 100/2 fold be laid together, and it is wanted to know the proper twist to put into the six cord which it has thus become. Let it be assumed that the operation was commenced with yarn of true counts; that is 100s, the doubling makes this into 100s two-fold, or counted singly 50s. But if measured and weighed out this yarn would not contain more than 48 hanks to the pound, and the reason of this is that the twining of the threads together reduces the length by about two hanks. Hence it is necessary, when a true length is required, to start with yarns higher in the actual than the nominal count. The three strands of the twofold 100s having, as we have seen, become, not 50s but 48, three of these laid together now reduce the counts to 16s; the square root of this number is 4, which multiplied by 3.75 gives 15, the number of turns per inch required at this stage. This process followed throughout will give satisfactory results. When the yarn is wanted to curl, it is usual to add about 20 per cent. to the twine obtained by this principle. For knitting yarns three folds, which are required to be soft, a rule in extensive use is to multiply the square roots of the yarns (single) by 2, and the result is the turns required. Crochet yarns follow the same rule, but require 2 for a multiplier. Embroidery cottons (four-folds) use the same standard number, 2, as the last-named.

APPENDIX.

ON STEAM BOILERS AND ENGINES.

Cotton mill boilers.- Dimensions.-Furnaces. -Flanging; boiler power; evaporative power.-To estimate the number of boilers required. -Inspection; cleaning; safety valves; low water alarms; pipes, feed, and steam connections. -Boiler setting, with illustrations.—Engines.Economizers.-Feed water temperature.-Position of economizer.— Chimney draught.-Oil consumption.-Driving.-Mechanical stokers.

TH

HE author is indebted to Mr. W. H. Booth, of the "Mechanical World," and formerly of the Manchester Steam Users, Association, for the following remarks upon steam boilers, engines, &c., in connection with which he has had an exte sive experience. Acknowledgment is also made to the proprietors of the abovə jurnal for the accompanying illustrations.

The boilers used to raise steam for either motive power or other purposes in the cotton trade are so universally of the Lancashire or internally-fired two-flued type, that we shall confine our remarks wholly to that type of boiler.

The making of boilers now ranks equal with, if not superior to the manufacture of stein-engines, and great care and skill are brought to bear upon their construction. The chief centres of the boiler-making trade in the cotton districts are Manchester, Hyde, Dukinfield, Blackburn, Bolton, and Preston. For some years past the standard size of Lancashire boiler has been 27 or 28 feet in length, with a diameter of 7 feet; and such a boiler, if double riveted, would be made from ths iron to stand 75 lbs. pressure, but during the three years ending December, 1883, the use of steam of 100 lbs. has become more common, and steel

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