310 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



fOcTODF.a, 



to ventilation is rendered certain and reg^iilar, being subject to the 

 l.iH- of cejitral forces, whiib is as fixed and determinate as that by 

 which a stone falls to the earth. 



In imitation of our Cornish method of estimating the lifting of 

 water from the mines, Mr. Brunton has, in Tal)le No. II., denomi- 

 nated the power necessary to propel the air by pounds falling 

 1 foot per minute; but in the use of this table it must be borne in 

 mind that the ]iressure per square foot is that due to the velocity, 

 and, to produce this current, an increase of 25 or 30 per cent, must 

 be made, as in ordinary mechanical operations, where 100 may re- 

 present the power or cause and 72 the eifect. 



II. The Desiccating Process for Drying and Seasoning Wood and 

 other materials. By Mr R. Davison, C E. 



Air. Davison stated that all other methods consisted in generat- 

 ing heat by simple radiation, or throwing off heat from a heated 

 surface, whether the surface be bi-ick flues, cockles, steam or hot- 

 water pipes. Heat is easily attainable in this way, and to almost 

 any grade of temperature; but heat is not the only essential re- 

 <iuired for drying, or why does the bleacher or laundress hang out 

 their articles to dry on a cold March morning. It is true that heat 

 facilitates the evaporation of tlio watery particles; but a current is 

 likewise necessary, otherwise all the water which is thus converted 

 into vapour will only tend to charge tlie chamber with steam; and 

 it is not until this steam has arrived at a certain excess, or pres- 

 sure, that it will make its escape, and the O])eration of drying 

 really commence. 



The amount of current obtainable in this way is proportioned to 

 the rarefaction, and quantity of air admitted and allowed to come 

 in contact with the heated medium: if little is admitted, there is 

 little current, an increased temperature, and likewise an increased 

 lohime of vapour, — or, vice versa, if a larger amount of atmospheric 

 air is admitted, thei-e will be a corresponding increased current, a 

 lessened temperature, and much less vapour. The ordinary cur- 

 rent obtainable in this way may be taken at 3 or 4. feet per second. 



To subject any article to a slow current of heat in a compara- 

 tively close chamber, or where there is an exceedinglj' small aper- 

 ture for the escape of vapour, whereby that article (whatever it 

 may be) is enveloped in an atmosphere of its own steam, is (to give 

 it its proper name) not drying, but stewing. If there is next to no 

 escape at all, as in the case of an oven, it is in reality baking. 



Mr. Davison stated that it is not only a moving but a rapid cur- 

 rent which is the great desideratum for all drying purposes; and 

 that it is the impulsion of atmospheric air, at tlie velocity of the 

 hurricane, or upwards of 100 miles per hour (or any other speed), 

 combined with the element of heat under perfect control, which in 

 fact constitutes the desiccating process. 



Mr. Davison next proceeded to describe the means by which the 

 two operations of current and heat are created and kept up; and 

 some applications whicli have been made of the process, together 

 with the practical results. — The drying apparatus, consisting of a 

 series of cast-iron pi])es, so united together as to form one con- 

 tinuous pipe bent vertically into an arch form, and set in a casing 

 of brickwork, with a common furnace, surrounded on the sides and 

 top by the pipes, comprehends at once the heating medium. The 

 cnirrent of air is created by a common blowing-fan, which can of 

 course be driven at any required speed either by hand or a steam- 

 engine. For all ordinary drying pui'poses, every thousand cubic 

 feet of space of the drying chamber requires 28 superficial feet of 

 heating surface in the pipes forming the furnace. 



So far as regards the construction of the apjjaratus, and the mode 

 of conve5'ing the heated air into, and the escape from, the cliamber 

 or stove, the same plan is carried out in all cases where mere dry- 

 ing is required, whether it be for wood, yarns, fabrics of all kinds, 

 starch, sugar, leather, paper, or indeed any article whatever which 

 simply requires moisture evaporated from it. The arrangement is 

 as follows — viz. one, two, or more, channels or ])ipes being laid in 

 or upon the floor of a building, whose sectional area corresponds 

 in the aggregate witli the heated outlet of the apparatus; the cur- 

 rents of air being driven into these by a fan, is allowed to escape 

 through small perforations made on the top or sides of the chan- 

 nels or pipes as the case may be, these perforations corresponding 

 again in amount of superficial area with the heated outlet : in this 

 way a uniform amount of current as well as temperature is distri- 

 buted throughout the chamber, and rises towards the regulating 

 orifices provided in the roof or sides of the building for the escape 

 of moisture. 



Air. Davison then proceeded to explain the application of the 

 desiccating process to the purifying of brewers' casks, which had 

 been adopted at some of the leading breweries in England and Ire- 

 land; at the brewery of Messrs. Guinness, of Dublin, upwards of 



one million casks in four years had undergone the process. He 

 then explained the application of the process to the drying or se4t- 

 soning of wood. 



The advantages of this process for drying wood are that it is a 

 true imitator of those elements which are said to be the best sea- 

 soners of wood, viz. the March wind with a summer heat, with this 

 addition — tliat a current of air exceeding by far that of any ordi- 

 nary wind, and a heat beyond that of any ordinary summer, ia 

 instantly and constantly at command, and kept up until every 

 grain of moisture is expelled. The greener the wood, the easier 

 and more perfect is the expulsion of moisture, and at the same 

 time the native strength of the fibre is secured by the immediate 

 evaporation of all vegetable juices or moisture likely to ferment 

 and carry on decomposition. The gums, instead of being removed, 

 are coagulated and hardened, and the texture of the wood gene- 

 rally (having been brought into its most complete state of aggre- 

 gation and density) is much less liable to imbibe atmospheric mois- 

 ture, and altogether less prone to decay. The colour of mahogany 

 and other fancy woods is not only preserved but improved, thus 

 avoiding everything approaching to a stain, as is too frequently 

 the case according to the ordinary method of seasoning such woods. 

 Shrinking is entirely obviated. The cost of desiccating is inex- 

 pensive — not exceeding the interest of money sunk in laying-up 

 wood to season in the ordinary way. — The process has been adopted 

 at the Tower of London for tlie seasoning of gun stocks; >and by 

 Messrs. Hall and Co., ship-builders, of Aberdeen, who have ap- 

 plied the process to seasoning wood for vessels, particularly the 

 decks of vessels; and also by numerous builders in London. 



The annexed Table will show the comparative strength and 

 deflection of desiccated specimens, and their duplicates after four 

 months' seasoning in the ordinary way. 



NO'i'E. — Tile above experiments, so far as ttiey relate to strenptii, are not otfereii as 

 ])ositively accurate, owing tn the npi-cimens being preparetl more witli a view of asier- 

 taininif tiie rate of seasoning Ity llie desiccating meliiod compare 1 ivltli natural seasoning. 

 For this purpc'se, tiie speciu'ens were in some instances piiined or pared, so as to liring 

 botlj to Itie same weijrtit. Tiie specimens, however, of which lliere was a (ionl)f., having 

 been left out of the Table, the above resialta may be considered sulficiently correct lor aU 

 piaclical purposeH. 



Before closing these brief remarks on this portion of the sub- 

 ject, it ought to be mentioned in reference to impregnating timber 

 with any preservative mixture, that timber which has thus been so 

 completely exhausted of all aqueous particles is in the best possible 

 condition to receive ingredients of any kind, but more especially 

 if timber instead of being allowed to cool after it is removed from 

 the desiccating chamber, is immediately plunged into a cold anti- 

 septic : it will be clear that a very considerable charging of the 

 pores must inevitably take place. A variety of fencing, railway 

 sleepers, keys, &c. having been treated in this way, and the very 

 best results having so far been observed, the plan is with confidence 

 recommended as one which ought to be more closely followed up. 

 In most cases, immersion, it is believed, will be quite unnecessary, 

 for if the desiccation of the timber is only complete, all that can 

 be wanted will be a thorough coating of some oleaginous fluid to 

 close the external pores. 



