DETAILS OE SCREW ENGINES.

■—

256

but having understood that a chemical actiontook place between the copper of the tubesand the sulphur employed in preparing theindia-rubber, and not being able to discover inthe new plans any advantage over “ Hall’s ”condenser, he adhered to this construction inthe condensers of the “ Mooltan.” As regardsthe action of the vulcanized india-rubber on thecopper tubes, the writer placed a piece of coppertube inside a piece of vulcanized india-rubbertube, and carefully washed and weighed thecopper tube every month, and found a gradualdecrease in its weight.

Mr. J. F. Spencer has often been alluded toin this work previously, in connection withthe “ cause and effect of surface condensers.”He observed, during the discussion followingMr. Humphrys’ paper, that he had also beenworking for many years at surface condensa-tion, but with the opposite system of pumpingthe cold water through the interior of the con-denser tubes, and condensing the steam on theoutside; and he was glad now to learn thepractical results of the working of “ Hall’s ”condenser in a large ship, as described in thepaper, the merits of that condenser havingcertainly not been fully appreciated.

In making a comparison between the twoplans of surface condensers—the one with thecondensing water outside the tubes and thesteam inside, and the other with the steamoutside and the water passing through theinside of the tubes—it was not necessary toconsider either the space occupied by the con-denser or the mode of making the joints at theends ot the tubes; because the space occupieddepended entirely on the size of tube employed,and the same size might be adopted whether

the water passed through the tubes or whetherit passed outside ; and the manner of makingthe joints by means of packing and screwedglands, as described in the paper, might beadopted for any plan of condenser. Settingthese considerations aside, therefore, he con-sidered an important practical difference be-tween the two systems lay in the circum-stance that, in order to examine a single tubeof a condenser on the construction shown inthe drawings, with the water outside the tubes,it was necessary to break a vacuum joint; andif such a joint were made again defectively at-sea in a hurry, air would leak in, the vacuumin the condenser would be diminished, and theefficiency of working impaired. Whereas whenthe water was inside the tubes, all the ends ofthe tubes were accessible by simply breakinga water joint, which was a matter of little con-sequence ; for if this jointwere made defectivelyat sea, the only result would be a small out-ward leak of water out of the condenser, whichwould not affect the working of the engine inthe slightest degree. In this respect, therefore,he thought a real practical advantage attendedthe plan of passing the water through theinside of the tubes.

A better distribution of water through thecondenser was also obtained by the same planof passing it through the tubes instead of out-side. In the condenser shown in the drawings,with the water outside the tubes, he thought itwould be almost impossible to pass the waterthoroughly and equally over every portion ofthe condensing surface; whereas the water in*side the tubes, by dividing the whole quantityof water into three or four currents distributedequally throughout the condenser, and by p r0 "