314 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[NOVEMBEB, 



^V^len removed the impression is developed by brushina: over a 

 warm solution of frallic acid, containinjr 20 ffi-ains in the fluid 

 (Hiiice, to wliicli a little stron^r acetic acid is added, and is then 

 fixed with a solution of hyposulphite of soda in the usual manner. 

 The present im])rovement consists in rinsings the paper in water 

 after the application of the solution of nitrate of silver, pressinj^ 

 out the superfluous moisture in folds of blottinf^-paper, and then 

 addiiifr a little more of tlie s(dution of nitrate of silver to tlie sur- 

 face of the paper. This is most conveniently eff'ected by pouring 

 a small quantity on the paper, and then pressing a glass-rod or 

 tube lightly over the paper, by which the solution is evenly dis- 

 tnlmted over the surface, and the contact of organic matter 

 avoided. The increased sensibility and improved cleanliness of 

 the paper consequent on this addition to the process are presumed 

 to depend on the removal by washing of tlie nitrate of potash 

 formed by the mutual decomposition of the salts on the surface of 

 the paper. 



/temarii.—Mr. Shaw remarked that the difficulty Mr. Brooke had ex- 

 perieiiced could only have arisen from some defect in the preparation of his 

 paper, and that had tlie difficulty a real existence, the means proposed to 

 remedy it were very doubtful. lie spoke confidently on the suhject, as by 

 hundreds of experiments he knew that the paper in question, when cartfully 

 prepared, preserved all its properties unimpaired for a much longer period 

 than that named by Mr. Brooke, and the failure of the paper in his hands 

 must have arisen from want of care in its preparation. Mr. Brooke's pro- 

 posed remedy was, he believed, defective in the following respect :— Mr. 

 Brooke assumed, that by adding bromide of potassium to the iodiile, a mix- 

 ture of the bromide and iodide of silver would be obtained on the paper; 

 hut such was not the case. If paper prepared with bromide of silver be 

 drawn through a solution of iodide of potassium, the whole of the bromide 

 is converted into iodide. The same took place with chloride of silver when 

 treated with iodide of potassium, so that Mr. Brooke was in error in suppos- 

 ing that he had formed any bromide of silver by the method he described. 

 This new paper was exactly the same as the old which he condemned. 



9. On the Heat of the ra/mrizatimi of Water. By J. P. Jouie. 

 The object was to point out the complex nature of the heat 



hitherto taken from the latent heat of steam. In the exact ex- 

 periments of Regnault 90.5° was found to be the quantity of heat 

 evolved in the condensation of steam saturated at 219°; of this 

 quantity 75° is the heat due to the vis viva communicated by the 

 pressure of the steam, leaving 890° as the true heat of vaporization 

 of water. In a perfect steam-engine supplied with water at '212°, 

 and worked at atmospheric pressure without expansion, 965° will 

 be the heat communicated from the fire to the boiler, 75° will be 

 the heat utilised by conversion into force, and the remainder 890° 

 will be the heat given out in the condenser. 



10. On a new Galvanic Buttery. By Mr. W. H. Wallenn. 

 The battery consists of zinc and cast-iron, the plates of the 



latter being brought very near to the former. The zinc jilate was 

 coated with lead, by being first immersed in acetate of lead, and 

 afterwards treated with mercury, the mercury being subsequently 

 volatilised by heat. The cast-iron was also prepared with carbon 

 in a way which was not easily gathered from the description, and 

 carbon was also described as dift'used in some way through the 

 dilute sulphuric acid which was used to excite it. The battery 

 Has said to be very active and very constant, and from the pro- 

 tecting action of the lead the zinc was eciniomised. The author 

 exhibited a plate of zinc which he described to have been used 

 for a considerable time, but which was nevertheless little acted on. 



Remarks — Mr. Shaw stated that the only novelty in the battery, except- 

 ing the use of carbon, which be did not comprehend, was the coating of the 

 zinc with lead, the effect of which, as he understood the author, was to pro- 

 tect the zinc not merely from what is called local action, but to defend it in 

 a great measure from the solvent power of the acid without impairing the 

 action of the battery. In the present state of electrical science, it vias im- 

 possible to receive such a view without a mass of evidence oiuch more exact 

 than that which had been brought forward. The elaborate researches of 

 Faraday had determined that the amount of electricity evolved in a voltaic 

 pair was in direct relation to the quantity of zinc oxidised and dissolved; 

 that is to say, the solution of an atom of zinc was accompanied by the 

 circulation of a definite amount of the electric force, and that whatever im- 

 peded the oxidation and solution of the zinc, diminished in the same ratio 

 the evolution of electricity. The electricity concerned in the decomposition 

 or formation of a compound was as definite a quantity as the material ele- 

 ments entering into its composition, and could be measured as accurately as 

 they could. This was established by a mass of evidence so overwhelming 

 as to be wholly unatfected by the general experiments brought forward. 



Mr. Wali.enn replied that he was still of opinion that his battery was 

 superior, and that the deflection of the galvanometer and the deposition of 

 copper, supported his opinion. 



Mr. Robert Hu.nt insisted on the importance of exact experiments; 

 nothing which he had stated could be put ia competitiou with the principles 



explained by Mr. Shaw, and he believed that by a more minute examination 

 of the subject he would find himself in error. Some of the parts of his 

 battery wbifh he regarded as new were not new ; and those that were, were 

 not improvements. 



lii'P'irt on recent Applications of the Wave Principle to the Prac- 

 tical Construction of Steam Vessels. By iMr. J. Scott Ri'sskij.. 

 - — (Read in the Section of Mathematical and Physical Science.) 



During the last year I have had more than one opportunity of 

 ajiplying the wave princi|)le to the construction of steam vessels. 

 There is one case, however, in which I have been able to apply it 

 to practice under circumstances of greater complexity and ditficulty 

 than have ever occurred to me, and where it has been successful in 

 overcoming difficulties to a greater extent and in a more decided 

 manner than heretofore. 



During the last year a very difficult problem was proposed to me. 

 It was this: — -To build a steam vessel that should be fast without 

 great length, a good sea-boat without drawing much water, and to 

 carry a great top weight and yet swim very light. Besides, this 

 vessel was to be able to go backwards as well as forwards equally 

 well; and, though a small boat, was to contain great accommoda- 

 tion. The problem is one to which the wave principle is far from 

 seeming peculiarly applicable. In the first place, it is well known 

 that the wave principle prescribes a different form of the bow from 

 that of the stern, in order to obtain most speed with least cost of 

 power. In the second place, it is known that a high speed re- 

 quires on the wave system a very considerably greater length than 

 was here allowed for the entrance of the vessel or the lines of the 

 bow. It would therefore seem at first to be a case that would prove 

 too difficult for the successful applicatiim of the wave system. 

 There is one more feature in the case which gives it interest. At 

 the same time the same problem was worked out by another party 

 on another plan of construction, not on the wave principle. Another 

 vessel was built under similar conditions, with engines of the 

 best construction, made by one of the most eminent engineers in 

 England. Both of these vessels were built at the same time and 

 tried under similar circumstances: therefore, here was a case in 

 which the practical value of the wave principle has been brought 

 to a test more direct and less questionable than any that was likely 

 to have occuiTed — and, therefore, more important to be placed on 

 the records of the British Association. The first question which 

 will naturally occur to a member of this Association who recollects 

 this principle will be this: How could you apply the wave principle 

 in a vessel made to go equally well both ways.^ The first answer 

 is ready — it is this, that the vessel cannot be made to go only one 

 way — seeing that in one case she would have a best possible bow 

 and a best possible stern, and in the other case could have neither. 

 The next point is this; that in both cases of bow and stern it was 

 necessary to have a compromise. Each required to be in turn bow 

 and stern, — this was accomplished in the following manner: — If 

 there be any point which has more forcibly struck me in the appli- 

 cation of the wave principle than another, it is the flexibility of 

 the wave principle, — the extent to which it admits of deviations 

 from its strict rules without losing the benefit of its assistance. If 

 it had unluckily been true of this system that it prescribed an 

 exact mathematical solid in its three dimensions (like Newton's 

 Solid of least Resistance), to which implicit adherence was impera- 

 tive on pain of losing all the benefit proffered, then, indeed, the 

 system would have been (like Newton's) of little use, from the fact 

 that, from causes independent of resistance, ships cannot be solids 

 of revolution, consistently with other qualities. The wave princi- 

 ple, on the contrary, possesses wonderful flexibility; first, from the 

 circumstance of its prescribing lines iti one plane only, and so leav- 

 ing the other two dimensions in the hands of the practical con- 

 structor, — so that the sections of the ^essel in one plane being 

 given by the system, the sections in two others are at the service 

 of the constructor. I had in this case to lay down for both ends 

 of the vessel, that which is best for a bow and that which is best 

 for a stern, at the given velocity. I had next to place relative 

 values on bow resistance and stern resistance. I had next to 

 single out from between those two lines one which, taken either as 

 bow or stern, would deviate least from either, and so have least 

 resistance on a mean of both directions. This, therefore, the wave 

 principle did; — it gave the limits, and gave also the choice of a 

 series of means all more or less suited to the purpose intended. I 

 have now shortly to state the practical details by which this pro- 

 cess was carried into effect and the results arrived at in conse- 

 quence. 



The engines of the vessel, as well as the vessel, had to be con- 

 structed by my partner, Mr. A. Robinson, and myself, and we were 

 enabled to adapt the one to the other with greater ease and cer- 

 tainty than in all likelihood we could have done had the engineer 



