2;6 



ON FIXING PHOTOGRAPHIC DRAWINGS. 



[1853- 



this article by quo'iag froni a sjientifis weekly contemporary tho 

 following report : — 



"The old flat flour-rnill ordinarily consists of a lowti- fixed 

 circular stone, and an upper revohing one, each of about 4 ft. C 

 in. in diameter. The wheat being introduced thiough an aper- 

 ture, is drawn in, and ground between the revohing and the 

 fixed surfaces. The average weight of these stones is about 14 

 cwt., and it is ordinarily found that the grinding surface pre- 

 sented, is so extended as to render the delivery of the flour 

 extremely slow and uncertain, nutwithstanding the great velocity 

 of the running stone, which is genei'ally 120 revolutions per 

 minute. The evil arising from this circumstance is, that the 

 flour, finding only a partial escape, is triturated and re-triturated 

 to the great ultimate injury of the meal. 



" Some idea of the power required to keep such massive 

 machines in operation may be gathered from the fact, that a 

 single pair of stones, 4 feet in diameter, require the power of a 

 four-hoi-se engine to maintain the needful speed. This enormous 

 power becomes necessary, in consequence of the great weiijht of 

 the ' top stone,' the rapid rate of revolution, and the very iai-ge 

 amount of fiiction pioduced by the process of grinding so gluti- 

 nous a substance as meal between such extended suifaces. 



" These are the principal objections to the old flat mill system 

 of grinding, which has been the univereal one in use in all parts 

 of the kingdom for a considerable time ; the only variation in 

 practice consisting in the motive power. iJost commonly steam 

 power is employed, but when the locality admits of its introduction 

 the cheaper and more uniformly certain agent, water, has been 

 brought into action. In all other respects, the mechanical detail 

 of the system has been uniformly the same. 



" The ' conical' mill is intended to obviate these defects ; and 

 a very few remarks will suffice to show that its inventor has not 

 only detected their causes, but has brought into operation a most 

 philosojdiic, and therefore successful, combination of grinding 

 and separating agencies, by which these defects have disap- 

 peared to an extent which leaves little to be desired. The 

 beneficial changes effected may be succintly enumei'ated. Fii-st, 

 the reduction of the weight of the running-stone from 14 cwt. to 

 1^ cwt, by phicing it beiieath instead of upon the fixed one; 

 second, the reduction of the size of the stones in the proportion of 

 3.34 to 1 ; and thirdly, the giving to the stones a new form — 

 that of the frustum of a cone. The advantage of lessening the 

 diameter and weight of a mass, of which the one is 4 cwt., and 

 the other 14 cwt., will be ajiparent, when it is considered that 

 its effective velocity is 120 revolutions per minute, and that this 

 velocity must be sustained against the enormous fiiction of the 

 grinding surfaces. The altered position of the running-stone 

 admits of a much more delicate adjustment of the 0]iposing sur- 

 faces, and gives to the miller an easy and effective control over 

 the most important portion of his operation. The conical form 

 facilitates the discharge of the flour, and ob\iates the clogging 

 und overheating of the old practice. In addition to these advan- 

 tages, by a judicious modification of the ordinary mode of dres- 

 sing, or rather by a combination of the mill with the dressing 

 machine, a perfect separation of the flour from the bran is effected 

 at the moment the grist escapes from the stone. The bran still 

 remains in the mill, and falls by its own gravity to a second pair 

 of stones in all respects resembling those already desciibed. 



"Both pairs of stones are mounted upon the same spindle, and 

 of course impelled by the same geaiing. The operation of the 

 lower pair need not be described ; they complete the process, and 

 leave nothing unconverted into flour which could add either to 

 the weight or the quality of the loaf. In considering this ar- 



rangement, we cannot fail to be stru;k with the analogy sub- 

 sisting between it and that which we observe in the construction 

 of the jaws of animals — a circumstance which assures us of its 

 philosophical superiority, 



" There were three trials as regarded the old srstem and the 

 new. The first experiment on the old mill gave a discharge of 

 16 lb of flour iu five minutes, which was equal to 192 lb per 

 hour; while upon the patent mill there wbs a discharge of 38 J- lb 

 in five minutes, or 462 lb ]ier hour. The dift'^rence, iherefore, 

 on that experiment wa?, against the old system, 270 lb per hour. 

 'J'lie second experi nent tried was even -more favourable as 

 regarded the new system. 



" Two conical mills worked against two on the flat principle 

 for an hour, ascertained exactly, and with the following results : 

 Conical mill (No. 1.) pioduced 8f bushels ; ditto, No. 2.) 7f 

 bushels; Flat mill (No. 1.) 3 busheb; ditto, (No. 2.) 3 bushels. 

 (See plate.) 



On Fixing Fhotagraphic Drawings. 



We have received fi-om an amateur, who states lie has " never' 

 yet seen the productions of any other person," some calotypes, 

 which are to a certain extent successful. They exhibit, however, 

 many of the faults which mark the productions of the inexperi- 

 enced operator; and we are therefore induced to ofl'er a few sug- 

 gestions which may be of assistance to our correspondent, and 

 othere similarly situated. 



In the first place, the specimens before lis bear the evidence of 

 having been obtained with a very imperfect lens — we should 

 judge from appearances, a lens which has not been raaile for a 

 Photographic Camera. Now, the peculiarconditions of the agent 

 by which these pictures are produced, demand the use of lenses 

 which have been constructed with due regard to certain known 

 principles; otherwise a perfectly flat field, and distinctness up to 

 the edges, cannot be obtained. 



It is a mistake to attempt to adopt an ordinary lens to a pho- 

 tographic camera; as, by so doing, failure must follow upon fail- 

 ure, and the production of a good photograph is rendered 

 impossible. 



Our correspondent complains of the injury which his pictures 

 recei\e in the ])rocess of fixing with the hyposulphite of Soda, 

 and regrets that some more j^erfect method cannot be discovered. 



We believe it will be difficult to discover any chemical agent 

 superior to the hyposulphite of soda, which, when properly em- 

 ployed, ensures the utmost degree of permanence to the photo- 

 graph under any circumstance of exposure. To place this clearly 

 before our readers is our object. 



1. The hyposulphites are remarkable for their property of 

 dissolving several of the salts of silver — such as the chloride and 

 iodide — fbriiiing with them compounds which are distinguished 

 by their peculiar sweetness. Negative Talbotypes consist of an 

 iodide of silver over all those parts which are not darkened: and 

 of metallic silver in a state of minute division over the darkened 

 portions. Positive piL'ture.s only differ fjom negatives in the 

 general use of the chloride of silver, instead of the iodide. In 

 either case the unchanged silver salt is to be removed, and tho 

 darkened portions disturbed as little as possible. In the ]irocess 

 of change under the influence of the solar radiations, oxide of 

 silver appears to be formed at first ; the oxygen is then liberated 

 and metallic silver is the final result. If much oxide of silver re- 



