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8 MARINE REVIEW. up with the steam into the upperdrum. When the air is not thus got rid of it causes rapid oxidation of the interior of the tubes. The causes of circulation are: First, difference in density of the water due to dif- - ference in temperature when the fires are first lighted. This circulation _ is very sluggish. Second, when the water is all at the same temperature and steam is being generated, but not with sufficient rapidity to cause a break in the continuity of the water, a comparatively sluggish circulation is set up by the entraining action of the bubbles of steam rising through the water. Third, when steam is generated with such rapidity that in some part of the circuit there is foam only present, a very rapid circulation takes place due to the difference in density between this foam and the continuous water in the down comers, internal or external. These con- ditions are illustrated in the accompanying diagrams. It is sometimes 'maintained that as the average density of the substance in the tube B, Fig. 1, is less than that of the substance in tube A, acirculation must take place in virtue of this. This is quite incorrect, as the hydrostatic pressure at the bottom of tube B must be just equal to that at the bottom of tube A, so long as the continuity of the water is not broken in either ofthem. The absurdity of this theory of circulation is at once seen, if we imagine a small cup inverted over each bubble of steam, as in--- dicated at C, in the sketch. By others itis assumed that the circulation especially in those boilers in which the tubes are not much greater than linch diameter, is of the kind shown in Fig. 2. In this case the water and steam are supposed to follow each other alternately in plugs as indi- cated. The author has spent a considerable amount of time in experi- menting with boilers built up of glass tubes about 2 feet in length, and varying in diameter from about half an inch up to 1}, inches, with var- ious rates of evaporation up to 9 pounds per square foot, but only when _the diameter of the tubes was reduced to 114 inches, and the tubes nearly vertical, was he able to obtain the conditions shown in Fig.2. In all cases, most of the circulation seems to be due to the upper parts of the 'tubes or the front headers, where these are used, or both, being filled with foam to the complete exclusion of continuous water. This is illus- trated in sketch, Fig. 3. The line A B shows the water level before start- ing, but as soon as rapid boiling has commenced the upper ends of the _ tubes and the upper headers are filled with foam, and there is a contin- uous flow of water along the upper drum. With tubes of 1 diameter and upwards, local circulation becomes very appreciable, especially in _ the upper of the three tubes shown. In this tube, while there is a con- tinuous upward stream of steam bubbles, there is also a continuous downward stream of water. The direction of flow of the waterin the middle tube, under some conditions, becomes alternating. The path of each bubble at any instant is, of course, in the direction of the resultant of all the forces acting on it at the instant. On this account the path may, when the tubes exceed a certain diameter, determined by the rate at which steam is being generated, be curved as indicated in Fig. 4. The size of the steam bubbles formed varies greatly with the rate at which steam is being generated. When the rate is great the bubbles are very much smaller-than when the rate is very small. The size of the bubbles also depends, of course, on the pressure under which the steam is gen- erated. 'So far as the action inside the tubes is concerned, the angle of in- clination of the tubes seems _ to be of little moment, so long asthe in- clination is not less than about 15 deg.,and not greater than about 70 deg. when the diameter of the tubes is about one inch, and it is probable that _the best inclination, in any given case, depends on the diameter of the tubes. When the tubes were horizontal, the water was almost entirely _ driven out of the lower ones. So far as the utilization of the radiant heat from the solid fuel on the grate is concerned, the boilers with tubes only slightly inclined to the horizontal have the advantage. It is often as- sumed that boilers with headers will not stand as much forcing as those in which each tube discharges directly into the upper drum. In practice it is found that there is no difference in this respect. "In designing boilers of this type, especial care should be taken that none of the tubes act as condensers for the vapors in the products of combustion, asif they do, the sulphurous acid thus deposited on the tubes may soon ruin the boiler. Boilers which are more or less trian- _ gular in form must occupy a greater space for a given power than those which are more or less rectangular in form, other things being equal This is obviously a matter of considerable importance in the case of _ marine boilers. "The main advantages which may be derived from the use of water tube boilers are due, firstly, to the comparatively small mass of water in them, and the consequent small loss due to steam raising, and, second] to the much higher average efficiency under greatly varying loads. This latter point is very well illustrated by the following abstracts from the tests of a Thornycroft boiler made by Professor Kennedy: At 89,1 horse power, efficiency of boiler 86.8 per cent. ; 282.1 horse power, 81.4 nee centy "449.2, horse power, 78.2 per cent.; 774.7 horse power, 66.6 nae cent." é ; Following the discussion of advantages derived from the use of water tube boilers the writer describes and illustrates the Babcock & Wilcox ) ------ LL Belleville, Thornycroft, Fleming & Ferguson, Normand and other gen. erators of the tubulous type that have come into marine use. Most of these boilers have been fully described with engravings in the Reyigy The Belleville boiler is described in our issue of June 30, 1894, the Fleming & Ferguson boiler in the issue of March 21, 1895, and the Babcock & Wilcox boiler in the issue of Oct. 11, 1894. Following is ay extract from a large table, which accompanies the paper, giving results of evaporative tests of various kinds of water tube steam boilers: RESULTS OF EVAPORATIVE TESTS OF VARIOUS KINDS OF WATER TURE STEAM BOILERS. Bogle gs | Ba Bo oa B y BS 3 a oO ots . ae S Lrg ae A HS H og ov @ @,| ag ag 2 | O85 25 & |Description oy Big lag "5 Description of steam eg ele of Oy dick ae boil i | .ag lused. | =| &9 oilers. es 3 § | coal used. 9 R: ao ag eee oO wm Ga os ~ belies g0.8| Fem a 3 Soul Hob ee vo o y ° SOB) Sou ay |. 9 = et? ee Thornycroft's water-tubeboiler| 22.7 | 1410 Welsh -- | 13:40 Babcock & Wilcox's ff 25 1403 |Scotch coal] 13.4 | 1238 ' fs 25 1403 sf 12.8. | 12.05 5 « 31 | 1380 | Anthracite | 12.8 | 11.99 " "6 23 1193 | Steam coal | 137 | 10.70 ss of 31.1 | 1426 Coke 6.8 10.05 " it 25 1610 Welsh 23 | 10.00 " << 15 860 Slack 24.6. 7.20 Belleville water-tube boiler......) 39.7 | 1264 Welsh a 11.71 & es weee| 39.7 | 1264 | Briquettes -- 10.83 De Naeyer water-tube boiler...| 40 1700 |Bituminous | 14.25 | 11.70 Herreshoff coil se ...| 26.0 | 485 | Anthracite 13.0 9.10 : " OG EeOG 485 sé 18.0 8.10 Heine's 66 vae| 194 869 | Steam coal} 18.8 9.00 Water tube boiler with vertical THDES ese. soe ectecccnseesacensersrecse 2.27 |" 928 ef 227 PES 88 Water tube boiler with pen- vadent twhesii. a7. csscie.s... K sireraid s 60 19.6 958 ff 21:9 8.10 Water. tube boiler with verti- cally inclined tubes............. 28 1600 oe 20.7 7.34 x ieee eee ee aed 17.2 | 870 Slack 34 7,02 Ward's water tube boiler......... = = Coal 15.5 8.28 Defects in Wisconsin's New Tax Law. Milwaukee vessel owners a few weeks ago secured the passage ofa lawin the Wisconsin legislature which fixes vessel taxes according to _ the net tonnage and age of vessels. It was thought that the law would recommend itself for adoption to the legislatures of other lake states, but a careful consideration of the measure shows that the assessment of taxes on a tonnage basis will be very unequal in many cases. There is already considerable complaint among vessel owners throughout the state on . account of this feature of inequality in the law. It is provided that vessels under five years of age pay $8 per net ton; vessels over five years of age and under ten years, $6 per net ton, and vessels over ten years of age $5 per net ton. Nowit will readily be seen that a big passenger steamer worth $200,000 to $250,000 will under such a law as this be required to pay no more in taxes than a wooden freight steamer worth only $60,000 to $75,000, as the government rules under which the tonnage of vessels is computed makes the tonnage of the largest passenger boats no greater than that of the freight steamer that carries 1,200 or 1,500 tons of freight. The same rules make the tonnage of schooners and tow barges much greater than that of steamers of the same dimensions, on account of engine room space being deducted in the case of the steamer, and thus such a law acts to the disadvantage of the poorer class of boats, and espe- cially the poorer class of sail vessels. Then, too, a valuable tug may escape taxation almost entirely, as the tonnage of tugs, which have no freight capacity, is very light. Evidently the new Wisconsin law is seri- ously defective as regards equality in taxation. Sailing Directions. Another book of sailing directions covering Lake Michigan, Green bay and the Straits of Mackinac has just been issued by the hydrographic office. This second part of the sailing directions for the lakes entire (the first book covered Lake Superior) will be followed in turn by Lake Huron with the St. Clair and Detroit rivers and Lake St Clair, and finally by Lakes Hrie and Ontario with the St. Lawrence river to Montreal. The books sell at $1 each and may be had from the MARINE REVIEW. When completed this work will be far more valuable than any "coast pilot" ever issued. These books are not recommended on account of any profit in their sale, as there is nothing in the sale of them, but they are certainly the best publications as yet issued by the hydrographic office in. con- nection with its work on the lakes. '