isao.") 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



287 



it is submitted to a second preparation, wliich is done by candle- 

 light, and as short a time as possible before the exposure ; it is, 

 however, still capable of givinj; good results several days after, 

 avoiding then, as much as possible, leaving it in a high tempera- 

 ture. 



We proceed therefore in this ])reparation by covering a glass 

 with aceto-nitrate of silver composed of 1 part of nitrate of silver, 

 2 parts of crystallizable acetic acid, and 10 parts of distilled water. 

 On this substance is deposited one of the sides of the paper, which 

 is allowed to imbibe until it has become perfectly transparent, 

 ■which is ascertained by raising it between the operator's eye and 

 the candle, after which it is dried between several folds of very 

 white blotting-paper, and left so until it has to be placed in the 

 frame, behind a sheet of very clean and dry paper, and between 

 two glasses, as in the moist operation previously described. 



The e.\posure to which we afterwards proceed next day, varies 

 according to the light and the power of the object-glasses, from one 

 to five minutes. 



On returning to work, the part of the paper which has been pre- 

 sented to the light is deposited in a saturated layer of gallic acid, 

 taking care to secure the other side from any trace of gallic acid 

 which would stain it. The image is gi-adually formed, and finally 

 acquires as powerful tones as can be desired ; it is then washed in a 

 great quantity of water, then parts into a solution composed of 

 ] part of bromide of potassium and 20 parts of water, in order to 

 dissolve the unreduced salts of silver, tlien again ivashed to remove 

 all traces of this bromide, whose action, by continuing, would 

 destroy the image, and finally dried between folds of blotting- 

 paper. 



Preparation of the Dry Albuminous Paper. — The paper ])repared 

 by albumen has analogous properties to that in the preparation of 

 which serum is used, but in an inferior degree ; like it, it remains 

 good for an almost indefinite period after preparation with the 

 iodide, but, after having been submitted to the aceto-nitrate of 

 silver, it can be scarcely kept beyond next day. The proofs given 

 by the preparation we are about to describe are admirable ; not so 

 fine as those on glass, they have more charms, because the contrasts 

 are less decided, and they possess more harmony and softness. We 

 think that it is a real acquisition for those who seek the eft'ects of 

 art in the results of photography. 



White of egg, to which have been added thirty drops of a satu- 

 rated solution of iodide of potassium and two drops of a saturated 

 solution of bromide of potassium to each white of e^^^ is beaten up 

 to a snow. It is left to i-epose until the snow returns to albumen 

 in the liquid state, and then filtered through silk or clear muslin, 

 the albumen being collected in a large and quite flat vessel. The 

 paper to be prepared is then deposited on the layer and left on it 

 for a few minutes. When it is covered with albumen, it is raised 

 by one of its corners, and allowed to drain and dry by suspending 

 it by one or two corners from a line. 



The preparation with the aceto-nitrate is, in every respect, the 

 same as that described for the paper prepared with serum; care must 

 be taken to dry it between two folds of blotting-paper only when 

 the paper has acquired complete transparency. It is put into the 

 frame for exposure in the same manner, the appearance of the 

 image and the rest of the operation is the same ; but the exposure 

 requires a longer time, generally four or five minutes. 



Preparation of the Positive Albumen Paper. — The positive ])aper 

 prepared with albumen gives somewhat less brillant proofs, but of 

 a richer tone, and of a more agreeable finish and transparency ; it 

 is prepared in the following manner: — To the whites of eggs is 

 added 25 per cent, (by weight) of water saturated with chloride of 

 sodium. The white of eggs is beaten into a snow, and filtered as 

 in the preceding preparation, only in this case the paper is left on 

 the albumen for only half a minute. It is then hung up to dry, 

 which is accomplished in six or eight minutes ; it is afterwards 

 deposited in a vessel containing 25 parts of nitrate of silver and 100 

 parts of distilled water. The paper is left in the bath at least six 

 minutes, and afterwards dried flat. 



CALEDONIAN CANAL. 



The annual report of the Commissioners for making and main- 

 taining the Caledonian Canal has just been printed. The report 

 gives an outline of the operations of the Committee till the 1st of 

 May last. 



The repair of those portions of the canal works which sufl^ered 

 from the unprecedented floods of January 1819, has been entirely 



completed in the past year, without interruption to the traffic. It 

 has also been thought advisable to secure the works against the 

 effects of a similar visitation, should such unhappily recur; and 

 with this view, under the advice of Mr. Walker, the south-east 

 bank of the canal above Doch-Garrock Lock has been strengthened, 

 and raised about two feet and a-half above the highest level of the 

 inundation. The gates of the lock itself are of such a height as to 

 require no addition. An increase of two feet in height has been 

 given to the canal bank of the reach above Aberchalder, and of 

 three feet to the banks above and adjoining Laggan Locks; but in 

 both these instances a corresponding addition to the height of the 

 masonry and lock-gates is required, which has not yet been eff'ected 

 from the apprehension of temporarily obstructing the navigation. 



Various additional accommodation and facilities for traffic have 

 been supplied along the line of the canal, which leave little now to 

 be desired for the convenience either of passengers or of trade. 

 At Clachnaharry, the timber jetty at the Sea Lock has been ex- 

 tended so as to obviate the risk of vessels grounding on the sloping 

 embankment: a similar jetty has been constructed at Corpach. 

 At Muirtown, the road of approach to the steamboat wharf ha* 

 been widened. The steamboat stations at each end of the canal 

 have been properly lighted: the roadway along the Dochfour em- 

 bankment has been completed and fenced. The only further 

 accommodations to which the Commissioners conceive that their 

 means might legitimately be devoted are, a small landing pier or 

 slip at Fort Augustus for vessels engaged in the local trade, and 

 an embankment track-path on the north-west side of the canal 

 between the Old and the New Gairlochy Locks, which are at 

 present connected only on the opposite side. The erection oi 

 landing piers at the difl^erent points where the steam-boots touch 

 on the Lakes, would be of much convenience, and the accommoda- 

 tion of a graving dock or patent slip for the repair of large vessels 

 at the eastern end of the canal is highly to be desired, but these 

 are rather subjects for individual enterprise. 



The sum of 10,000/., granted by parliament for the repair of the 

 damages to the canal works, occasioned by the floods of January 

 1S49, was issued in August last, and there is no reason to doubt 

 that the anticipations of its sufficiency for the entire restoration 

 of the works, and also for the completion of the several precau- 

 tionary measures above alluded to, will be verified. 



With regard to the Crinan Canal, the report states that the con- 

 dition of this navigation has been much improved by various im- 

 portant repairs. The upper gates of the summit lock at Cairnbaan 

 (No. 8), and also of the second lock at Crinan (No. It), have been 

 renewed. By means of a small dredging apparatus fitted to tlie 

 canal barge, an additional depth of near two feet has been gained 

 in the entrance to the canal through the harbour of Ardrishaig, 

 greatly diminishing the period of detention (sometimes five or six 

 hours), long complained of by masters of vessels, especially of 

 steamers, which drawing ordinarily about seven feet water, were 

 previously unable to enter or depart from the canal after half-ebb 

 on the falling tide, or before half-flood on the rising tide. The 

 dredging apparatus has also been usefully applied in restoring the 

 canal to its full depth at spots where, as at Dunardry, the deposit 

 from burns discharging into it had greatly encumbered the bottom. 

 The reduction of dues upon the navigation, which was announced 

 in the last report, has not diminished the revenue, although the 

 tariff' of charges on the principal articles conveyed was reduced by 

 nearly one-third. The revised tariff' was in force for the last nine 

 months only of the year 184.9, during which time the increased 

 resort of sailing vessels produced 1135/., as compared with 1113/. 

 in 1848. Out of 729 vessels entering or clearing from the Clyde 

 from or to northern ports, and capable of passing the canal, only 

 353 (or 48^ per cent.) took the passage round the Mull of Cantyro, 

 whereas in the corresponding period of 1848, that course was 

 adopted by rather more than 62 per cent, of the vessels under 

 similar circumstances. In the months of January, February, and 

 March 1850, this proportion was reduced to about 21 percent., but 

 it increases as the approach of summer diminishes the danger of 

 the more exposed and circuitous course. The dues on steamboats 

 were not reduced at the time of the revision of the general tariff; 

 but by an alteration sanctioned in the course of the month of .May 

 in the present year, the commissioners have authorised a reduction 

 of the tonnage rates leviable upon steamboats from 9rf. to Hd. per 

 ton, and also of the harbour rates at Ai-drishaig and Crinan from 

 \d. to ^rf. per ton. 



