114 



NATURE 



[April 5, 1917 



speed than reciprocating engines, the necessity of 

 seeing that the propellers were suitable not only as 

 regards form, but also as regards theii being in proper 

 mechanical balance, has received considerably more 

 attention. Experiments have been carried out m two 

 destroyers and a Town class cruiser built at the 

 Commonwealth Naval bockyard at Sydney. The paper 

 describes experiments made by rotating the propeller 

 at speed on spring bearings, noting the vibration and 

 removing material froni certain parts of the blade and 

 even the boss. From subsequent observations on the 

 ships it was apparent that there was a decided im- 

 provement. The problem to be solved is by no means 

 easy, since removal of material from the blades of a 

 propeller has the effeci of altering; the pitch, and naval 

 architects, as a rule, have very stringent specifica- 

 tions regarding the exactitude of tho pitch of a pro- 

 peller. 



Sir George Greenhill contributed a paper on the 

 theory of wave-motion on water. In this paper the 

 author discusses matnematically the trochoidal wave 

 as treated by Rankine, Mr. John H. Macalpine gave 

 particulars of marine applications of reduction gears 

 of the floating-frame type. The success of this type 

 of gear appears to be ve«-y marked. The first floating- 

 frame gear was installed at Granite City, Illinois, in 

 191 1 ; when examined on April 30, 1916, the scraper 

 marks were still visible on the gear teeth. Originally 

 these marks were of imperceptible depth. 



Messrs. P. A. Hillhouse and W. H. Riddlesworth 

 presented a paper on la-, nching. This paper contains 

 an account of some intf resting experiments made at 

 the Fairfield Shipbuilding Yard. A model of the ship 

 was constructed and arranged in all respects to be a 

 reduced copy. Model ways were constructed and a 

 tank arranged with water at proper tide level. By 

 these means valuable information was obtained re- 

 garding the motion of the ship during launching. 

 The authors make an interesting suggestion whereby 

 an accurate record of the complete motion of the 

 actual vessel from start to finish might be obtained by 

 means of the kinematograph. Two machines would 

 be required, one placed near the stern of the vessel 

 when on the slip, and the other somewhat less than 

 the length of the vessel further aft. Both would stand 

 at a convenient distance away from the vessel's side, 

 and would have their axes at right angles to the 

 middle line of the berth. In the field of view of 

 each, two uprights would be placed as near to the 

 vessel's side as possible, and on each upright a vertical 

 scale of feet would be clearly marked in black and 

 white. On the ship's side would be painted a con- 

 tinuous longitudinal white line crossed by short ver- 

 tical lines numbered in succession from either end. 

 As the vessel moved the cameras would record con- 

 tinuously the movements of the white line, in relation 

 to the ship and to the water level and ground ways, 

 and the whole motion could be reconstructed. If, in 

 addition, there could be piaced in front of each 

 camera a large clock-face with seconds pointer, the 

 two sets of photographs could be correlated and a 

 record of velocities obtained. 



BRITISH FILTER-PAPERS. 



AS is well known to laboratory workers, in pre- 

 war days the better kinds of filter-paper used 

 in chemical operations were not produced in this 

 country. They were imported chiefly from Germany 

 and Sweden. In particular, the so-called " ashless " 

 filters, from whl..h most of the mineral matters have 

 been extracted by treatment with hydrochloric and 

 hydrofluoric acids, had made the name of one German 

 firm familiar in probably every chemical laboratory 

 of importance throughout the kingdom. The out- 

 NO. 2475, VOL. 99] 



break of war, however, stopped the supply of German 

 filters, and British paper-makers turned their atten- 

 tion to meeting the demand. 



The qualities required in filter-paper depend upon 

 the purpose to which it is to be applied. Thus for 

 certain technical operations, such as the filtration of 

 oils and fruit juices, a soft paper of open texture is 

 desirable. Further, as such paper is often used for 

 filtration under pressure, a high degree of elasticity 

 is required in it to prevent fracture. In analytical 

 work, on the other hand, whilst a paper with open 

 texture which filters rapidly is preferable for floccu- 

 lent precipitates like ferric hydroxide, a close-texture 

 paper is required for the retention of fine precipitates 

 such as barium sulphate. Moreover, the proportion 

 of mineral matter is important. Compounds of cal- 

 cium and iron, frequently with a little copper, and 

 sometimes silica and alumina, are the chief mineral 

 impurities found in filter-paper; and for accurate 

 quantitative work the amount of these should be small. 

 Indeed, it should preferably be so small as to be 

 negligible except where a high degree of exactitude 

 h required. In any case, it should be definitely 

 known, and ought always to be stated on the packets 

 of filters by the makers. , , 



The ability to retain fine precipitates, a minimum 

 proportion of ash, and reasonable rapidity of filtra- 

 tion are thus the chief desiderata in the best filters 

 for chemical laboratory purposes. The last alone is 

 sufficient in manv technical operations. Discussing 

 this question in' the Analyst some months ago, 

 Messrs. Bevan and Bacon indicated that for paper 

 required to filter with moderate rapidity the ratio of 

 the volume of the paper to that of its constituent 

 fibres should be about 35 to i. It does, in tact as 

 a rule vary between the limits 3 and 45 to i. Fin- 

 holes " are sometimes found in paper having this 

 ratio or "bulk" (as the technical term goes); they 

 are attributable to faults in the milling. 



Some time ago specimens of the filter-papers now 

 produced in this country were supplied to us by three 

 manufacturing firms, namely, Messrs. W. and K. 

 Balston, Ltd., Maidstone; Messrs. J. Barcham Green 

 and Son, Maidstone; and Messrs. Evans, Adlard and 

 Co Ltd., Winchcombe. Judging by the reports fur- 

 nished with certain of the papers, supplemented bv 

 tests applied in actual working practice, a number of 

 the samples compare quite well with the foreign 

 filters which they have replaced. It is evident that 

 a serious endeavour is being made to produce filters 

 which will compare favourably in quality with even 

 the best of those hitherto imported, and the efforts 

 appear to have met already with a considerable 

 rneasure of success. Naturally, it will take time and 

 careful study completely to outvie the foreign articles, 

 which are the result of long specialisation. Uniformity 

 of product is an important point to aim at, so that 

 the user may know that he can rely upon the con- 

 stancy of the quality. There is no obvious reason 

 why British paper-makers should not, with proper 

 technical advice, compete successfully with foreign 

 manufacturers in this branch of industry, and, in tact, 

 there is good reason to believe that they will do so. 

 In this matter, as in so many others, we ought not 

 to have to revert to the status quo ante helium. 



COMPULSORY CONTINUATION CLASSES. 



THE final report of the Departmental Cuirnniuee 

 on Juvenile Education in Relation to Employ- 

 ment after the War has just been issued (Cd. 85 12, 

 price 6d. net). 



The terms of reference of the committee were : 

 To consider what steps should be taken to make 



