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If nitrate of silver； specific gravity 1。200 be added to ferro…tartaric acid； specific gravity 1。023； a precipitate falls； which is in a great measure redissolved by a gentle heat； leaving a black sediment； which； being cleared by subsidence； a liquid of a pale yellow color is obtained； in which the further addition of the nitrate causes no turbidness。 When the total quantity of the nitrated solution added amounts to about half the bulk of the ferro…tartaric acid； it is enough。 The liquid so prepared does not alter if kept in the dark。 Spread on paper； and exposed wet to the sunshine （partly shaded） for a few seconds； no impression seems to be made； but by degrees； although withdrawn from the action of light； it developes itself spontaneously； and at length becomes very intense。 But if the paper be thoroughly dried in the dark； （in which state it is of a very pale greenish yellow color；） it possesses the singular property of receiving a dormant or invisible picture； to produce which from thirty to sixty seconds' exposure to sunshine is requisite。 It should 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the ultimate effect less striking； but a picture begins to be visibly produced； which darkens spontaneously after it is withdrawn。 But if the exposure be discontinued before this effect comes on； an invisible impression is the result； to develope which all that is necessary is to breathe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 alc