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- MARINE This Season’s Trade Will Equal That of 1890. Notwithstanding a delay of nearly two months in the open- ing of navigation last spring, it is more than probable that the season’s business in the aggregate will be about equal to that of 1890. The Sault canal records show that. the freight traffic through the canal up to September 1 is g2 per cent. of the same for last season. Larger and faster vessels, the big grain crop and other conditions will serve to make the volume of business in six months this season equal that of seven anda half months in 1890. The traffic through the Sault canal during August was larger than ever before-in the history of the canal for one month. Of steam vessels 1,229 passed through, of sail vessels 434, and of rafts and unregistered craft 57, a total of 1,720. ‘Thetotal regis- tered tonnage was 1,460,144, total freight tonnage 1,545,607, number of passengers carried 8,099. The total number of lock- ages was 828. The increase in traffic over the corresponding month in 1890 was, in registered tonnage 207,366, freight ton- nage 134,313, passengers 327, passages 165. It exceeds the traf- fic for the previous largest month (July, 1891) by 16,054 net tons, although the number of vessels passing and_ the registered tonnage was slightly less than during that month. The tonnage movement through the canal was divided a follows: j Description. East-bound West-bound. Coalici.csss SGuce kins kg NuAcesaciswansunan suenewesnns 428,842 tons. BGT iss socks caseanvetanecssavesecsanis 553,475 bbls. 100 bbls. AORN a iwate on hes ncosebiae ssh arkcc at ab ses ape cmeicnd 27,000 bu ASOMMM siasschaaicapsssanvarevencspocnssnens P52, 50L DU, 2 cccssusseess WHERB SIN ass E542 325 OUT SO eette Building. Stoneisiccssesecc.ccpssb as BOS 1 Lows 157 a taekics one SHOE sash cu sk-vasasenc snares eeces BONS TOMS. 5. Fics cnaverenes Maniifacinred Gon... ....0.: cscs. Gdewes om ove : 3,980 tons. ATION OCC cass cicionessechcsasrssscsce nn sss 820,738) 4ONSe ce csexsseswuten COO Te OT EAs as Seo 6,301 tons, as. SSBC ircoetes ck ae da peeieas oo c0h sasdisne des “aems esis wide 29,291 bbls. DAO T aitensnaxscs cp scsseesurssaicvs'ss BOAR MPR got saneetesnn Unclassified freight......... eceee 10,000 tons. — 43,871 tons. PASHRALO CES Gor sc seers ss ssisoter cence se ASA PES A QST : bal . . od No silver ore was shipped east by water during August al- though there is usually a fair movement in that mineral. Bad Spot Near Grosse Point. In the fall of 1889 the steamer Chemung struck an obstruc- tion in Lake St. Clair and sustained serious damages. It is now more than probable that damages recently sustained by the steamers Corona and Hudson were caused by the same _ obstruc- tion, although there is little use of masters trying to avoid it from the desciption of the locality furnished, as it is directly in the channel leading to Grosse point light-ship and any of the deep laden steamers may be unfortunate enough to run onto it at any time. The master of the Hudson, whose boat broke her wheel on the obstruction a short time ago, says that when the a¢cident occurred he was bound down Lake St. Clair and about fifty minutes out from the canal, steering S. W.%S. He locates the wreck or sunken log, as he calls it, N. F. % N. from Grosse point light-ship. An extract from the log of the Chemung, says: “Entered St. Clair canal 10:30 a. m; checked very slow, water being low; clear of the canal 10:48 a. m.; shaped course S.W. ¥% S. The wind was southwest, light with fog. The engine was then making 45 turns a minute; 11 a. m. engine was making 62 turns a minute At 11:25 the fog lifted and we made Grosse point light-ship on our starboard bow. We hauled S. W. % S., heading into it, and at 11:35 a.m. struck bottom forward.” It will be seen that the extracts from the logs of both vessels are very close to being alike as to the location of this obstruction, but a sunken log or a small portion of a hull of some kind can not be found from the directions given, unless it is by sweep- ing in the vicinity. Gen. Poe and Commander Heyerman will probably follow this plan in an attempt to find the spot, as an effort on the part of Commander Heyerman with the light-house steamer Marigold has failed. Many of the Cleveland vessels carry buoys to be thrown overboard when an obstruction of this kind is encountered and they should be carried on all yessels. Any kind of a mark will do temporarily. Before the Inspector. EDITOR MARINE REVIEW :—In my last communication, dealing with that which may be expected by the lake engineer who seeks a license from any of the coast representatives of the steamboat inspection service, I re- ferred to the surface condenser, but I have since been asked why I didn’t give more details in regard to it, as that is one of the principal points that lake engineers are not familiar with. Where feed water is taken from a surface condenser it is best to allow a thin coating of scale, about as thick as letter paper, to form on the internal surfaces of the boiler. This scale protects the metal of the boiler from the pure distilled water which has a tendency to attack the metal and develop pitting and internal corrosion; a tendency which is heightened by the cylinder oil that goes in with the feed water. As a few of our engineers have learned to their sorrow, this oil in it- self is a dangerous element in boilers. The oil and other foreign matters precipitated within the boiler combine and form cakes which eventually sink and adhere to the tubes, or furnace crowns, thereby preventing the water from coming in contact with the metal, and the result is a burned and blistered plate, or possibly an explosion. The collections of oil are more dangerous in boilers using fresh water than where salt water is used, as the gravity of fresh water being less than salt water the cakes or slugs of foreign matter will sink sooner; and then, as I memtioned in my last article, the salt has a tendency to cut up and granulate the heavy collec- tions of oil. : Where surface condensers are used it is also a good plan to dissolve 15 or 20 pounds of salsodaand put it through the condenser and into the boiler frequently ; and especially just before blowing off. The sal soda causes the oil to saponify, or become soap, and it can be more readily blown through the surface blow pipe. ie Another cause which hastens the pitting and grooving in boilers con- nected with surface condensers, is the brass tubes in the condenser and the copper pipes in connection with the feed pumps, which together with the water form galvanic action, the water acting asa conductor. To counteract this galvanic action, slabs or pigs of pure zine are sus- pended within the boiler. Asaresult, the zinc is attacked instead of the iron, and it wastes away very rapidly and requires to be frequently renewed. It.is well to become familiar with the care of boi'ers using water from surface condensers, as the inspector will undoubtedly ask you in regard to this. : s It is also well to remember that latent heat is heat that does not ‘affect the thermometer, and which expands itself in changing the nature of a body, such as turning ice into wafer and water into steam. Bodies get latent heat when passing from a solid to a liquid, or from a liquid to a gaseous state. Latent heat can be recovered by bringing the body from a gaseous to liqued, or from,a liqued to a solid state. A thermal unit is the heat necessary to raise the temperature of one pound of water from 39° to 40° Fahrenheit. Water is at its greatest density when its temperature is 39° Fahren- heit. It expands if either heated or cooled from that temperature. The meaning of zero is empty or nothing, and when applied to temperatures absolute zero means no heat. It is the temperature at which gases would become solids, as water becomes ice. Absolute zero is 461.22° below Fahrenheit’s zero, All bodies contain heat when above that temperature. It may seem to some that these things do not come under the head of practical engineering, but they are all among the things regarding which the inspectors propound questions, and they tend to show whether aman takes interest enough in his profession to study the subjects per- taining to it. The time has arrived when it is necessary for marine engineers to have a smattering of science, and those who will not acquire it have no one to blame but themselves. Steam engineering has received more at- tention from capable writers than any other trade or profession in exis- tence, and the man who will not avail himself of opportunities to ac- quire a knowledge of the scientific as well as the practical branch of his profession can already see himself droppirg behind in the race for success. Cleveland, Ohio, Sept 8, 1891. F. B. SMITH. The llst of vessels to which the bureau of navigation assigned official numbers during the week ending Sept. 5 contains only one lake craft, the yacht Gertie of Detroit—8.16 tons gross, 7.76 tons net, No. 86,169. Some boilers recently made in Pittsburgh are ro feet diameter and 30 feet long with 234 flues, 4 inches diameter 30 feet long. The shells are of steel one inch thich, and it is claimed they are the largest ever made in Pittsburgh. The rest of the country may as well be included. The boilers of the Australia made here contain about the same capacity, 2000 cubic feet, and were believed to be the largest ever made in this country at the time, two years ago.—Journal Industries, San Francisco.