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hould not be exposed too long； as not only is the ultimate effect less striking； but a picture begins to be visibly produced； which darkens spontaneously after it is withdrawn。 But if the exposure be discontinued before this effect comes on； an invisible impression is the result； to develope which all that is necessary is to breathe upon it； when it immediately appears； and very speedily acquires an extraordinary intensity and sharpness； as if by magic。 Instead of the breath； it may be subject to the regular action of aqueous vapor； by laying it in a blotting paper book； of which some of the outer leaves on both sides have been dampened； or by holding over warm water。
II。 ENERGIATYPE。
Under this title a process has been brought forward by Mr。 Hunt。 It consists of the application of a solution of succinic acid to paper； which is subsequently washed over with nitrate of silver。 The image is then to be taken either in the camera or otherwise； as required； and is brought out by the application of the sulphate of iron in solution。 Although this process has not come into general use； its exact description may be interesting to the general reader； and we therefore subjoin it。
The solution with which the paper is first washed is to be prepared as follows： succinic acid； two drachms； common salt； five grains； mucilage of gum arabic； half a fluid drachm； distilled water； one fluid drachm and a half。 When the paper is nearly dry； it is to be brushed over with a solution of nitrate of silver； containing a drachm of the salt； to an ounce of distilled water。 It is now ready for exposure in the camera。 To bring out the dormant picture it is necessary to wash it with a mixture of a drachm of concentrated solution of the green sulphate of iron and two drachms and a half of mucilage of gum arabic。
Subsequently； however； it has been found that the sulphate of iron produces upon all the salts of silver effects quite as beautiful as in the succinate。 On the iodide； bromide； acetate； and benzoate； the effects are far more pleasing and striking。 When pictures are produced； or the dormant camera image brought out； by the agency of sulphate of iron； it is remarkable how rapidly the effect takes place。 Engravings can be thus copied almost instantaneously； and camera views obtained in one or two minutes on almost any preparation of silver。 The common sulphate of copper solution has the same property。
III。 CHROMATYPE。
Many efforts have been made to render chromatic acid an active agent in the production of photographs。 M。 Ponton used a paper saturated with bichromate of potash； and this was one of the earliest photogenic processes。 M。 Becquerel improved upon this process by sizing the paper with starch previous to the application of the bichromate of potash solution； which enabled him to convert the negative picture into a positive one； by the use of a solution of iodine； which combined with that portion of the starch on which the light had not acted。 But by neither of these processes could clear and distinct pictures be formed。 Mr。 Hunt has； however； discovered a process which is so exceedingly simple； and the resulting pictures of so pleasing a character； that； although it is not sufficiently sensitive for use in the camera； it will be found of the greatest value for copying botanical specimens； engravings； or the like。
The paper to be prepared is washed over with a solution of sulphate of copperabout one drachm to an ounce of waterand partially dried； it is then washed with a moderately strong solution of bichromate of potash； and dried at a little distance from the fire。 Paper thus prepared may be kept any length of time； in a portfolio； and are always ready for use。
When exposed to the sunshine for a time； varying with the intensity of the light； from five to fifteen or twenty minutes； the result is generally a negative picture。 It is now to be washed over with a solution of nitrate of silver； which immediately produces a very beautiful deep orange picture upon a light dim colored； or sometimes perfectly white ground。 This picture must be quickly fixed； by being washed in pure water； and dried。 With regard to the strength of the solutions； it is a remarkable fact； that； if saturated solutions be employed； a negative picture is first produced； but if the solutions be three or four times their bulk of water； the first action of the sun's rays darkens the picture； and then a very bleaching effect follows； giving an exceedingly faint positive picture； which is brought out with great delicacy by the silver solution。
It is necessary that pure water should be used for the fixing； as the presence of any muriate damages the picture； and here arises another pleasing variation of the Chromatype。 If the positive picture be placed in a very weak solution of common salt the image slowly fades out； leaving a faint negative outline。 If it now be removed from the saline solution； dried； and again exposed to sunshine； a positive picture of a lilac color will be produced by a few minutes exposure。 Several other of the chromates may be used in this process； but none is so successful as the chromate of copper。
IV。 ANTHOTYPE。
The expressed juice； alcholic； or watery infusion of flowers； or vegetable substances； may be made the media of photogenic action。 This fact was first discovered by Sir John Herschel。 We have already given a few examples of this in the third chapter。
Certain precautions are necessary in extracting the coloring matter of flowers。 The petals of fresh flowers are carefully selected； and crushed to a pulp in a marble mortar； either alone or with the addition of a little alcohol； and the juice expressed by squeezing the pulp in a clean linen or cotton cloth。 It is then to be spread upon paper with a flat brush； and dried in the air without artificial heat。 If alcohol be not added； the application on paper must be performed immediately； as the air （even in a few minutes）； irrecoverably changes or destroys their color。 If alcohol be present this change is much retarded； and in some cases is entirely prevented。
Most flowers give out their coloring matter to alcohol or water。 Some； however； refuse to do so； and require the addition of alkalies； others of acid； &c。 Alcohol has； however； been found to enfeeble； and in many cases to discharge altogether these colors； but they are； in most cases； restored upon drying； when spread over paper。 Papers tinged with vetegable colors must always be kept in the dark； and perfectly dry。
The color of a flower is by no means always； or usually； that which its expressed juice imparts to white paper。 Sir John Herschel attributes these changes to the escape of carbonic acid in some cases； to a chemical alteration； depending upon the absorption of oxygen； in others； and again in others； especially where the expressed juice coagulates on standing； to a loss of vitality； or disorganization of the molecules。 To secure an eveness of tint on paper； the following manipulation is recommended：The paper should be moistened on the back by sponging and blotting off。 It should then be pinned on a board； the moist side downwards； so that two of its edges （suppose the right…hand and lower ones） shall project a little beyond those of the board。 The board then being inclined twenty or thirty degrees to the horizon； the alcoholic tincture （mixed with a very little water； if the petals themselves be not very juicy） is to be applied with a brush in strokes from left to right； taking care not to go over the edges which rest on the board； but to pass clearly over those that project； and observing also to carry the tint from below upwards by quick sweeping strokes； leaving no dry spaces between them； but keeping up a continuity of wet spaces。 When all is wet； cross them by another set of strokes from above downwards； so managing the brush as to leave no floating liquid on the paper。 It must then be dried as quickly as possible over a stove； or in a warm current of air； avoiding； however； such heat as may injure the tint。
In addition to the flowers already mentioned in my third chapter； the following are among those experimented upon and found to give tolerable good photographic sensitives。 I can only enumerate them； referring the student； for any further information he may desire on the subject； to Mr。 Hunt's work； although what I have said above is sufficient for all practical purposes； and any one； with the ambition； can readily experiment upon them； without further research； on any other flower he may choose。
Viola Odorataor sweet sented violet； yields to alcohol a rich blue color； which it imparts in high perfection to paper
Senecio Splendensor double purple groundsel； yields a beautiful color to paper。
The leaves of the laurel； common cabbage； and the grasses； are found sufficiently senstive。
Common Merrigold yields an invaluable faecula； which appears identical with that produced by the Wall…flower； and Cochorus japonica mentioned before； and is very sensitive； but photographs procured upon it cannot be preserved； the color is so fugitive。
From an examination of the researches of Sir John Herschel on the coloring matter of plants； it will be seen that the action of the sun's ray