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This mixed, in equal proportions with John Roach's quick, forms an excellent chemical combination. For this purpose, take one and a half ounce of each, to which add ten ounces water, for warm weather, or from six to seven for cold. Pour the whole into a large box, and it will work from two to four months.

I am now using (l849) one charged as above which has been in constant use for three months, and works uniformly well.

The above is right for half or full size boxes, but half of it would be sufficient for a quarter size box.

Coat to the first shade of rose over iodine, change to a deep rosy red over quick, and black about one tenth the first.

I would not now recommend the addition of "John Roach s quick,"as I believe equally good results can be produced without it.

This liquid is now used by many, and is very good for taking views.

Lime Water Quick.--This mixture is more used at present than all the other liquids ever introduced. It produced the most uniform results, giving the fine soft tone so characteristic in pictures produces from accelerators containing chlorine.

To one quart of lime water (this can be had of any druggist)add one and a half ounce of pulverized alum.

This should be shook at intervals for twenty--four hours;then add one ounce of chloride of iodine and three fourths ounce of bromine.

Lime Water.--This is easily prepared by putting lime into water, say a piece of quick-lime about the size of an egg into one quart of water.

This should be shook occasionally for two or three days and allowed to settle, when the water can be poured off and used.

Use.--To one part of quick add six parts of water; coat to a light yellow over the iodine, to a rose color over the quick, and recoat about one tenth.

The above coating may be increased or diminished, it matters not, so that there is not too much, and the proper proportions are preserved.

Some add to the above a small quantity of magnesia, say about a teaspoonful to the quart of liquid.

Liquid Accelerator, No. 2.--The following was for a long time used by one of the first houses in the United States, and probably was one of the first liquids ever used.

It produces a fine-toned picture, but is not considered as sure as the lime water quick:

Take rain water one quart, add pulverized alum until it is a little sour to the taste, and a small piece, say one half inch square, of magnesia.

Filter through paper, and add chloride of iodine one half ounce, bromine sufficient to take it up, which is a little less than half an ounce.

Charge with one of quick to six of water; coat over iodine to a soft yellow, nearly, but not quite, bordering on a rose;over quick to a dark purple, or steel, and back one sixth to one tenth.

Wolcott's American Mixture.--Van Loan Quick.--This mixture was first formed and used by T. Wolcott & Johnson and gained great celebrity for its productions. I have now a bottle hermetically sealed that contains about a half ounce of this mixture prepared in 1841 by John Johnson, now a resident of this city, and the former partner of Mr. Wolcott.

The preparation of this mixture, as furnished by Mr. Johnson himself, is given as follows:

"One part of bromine, eight parts of nitric acid, sixteen parts of muriatic acid, water one hundred parts.

This mixture should be allowed to stand for several days;it improves by age.

"Use.--A few drops say, 6 to 12, of this mixture, should be put into about 6 or 8 ounces of water; it will require frequent replenishing by the addition of a few more drops. The plate should be coated over the dry iodine to a red just bordering on a slate.

and then exposed to the mixture only sufficiently long to change the color.

If this is not done in less than six seconds it is not strong enough.

Re-coat over the iodine full one fourth as long as first coating."This exceedingly volatile compound is difficult to control from its instability; it is but little used. The impressions successfully produced by this mixture are very brilliant, and possess a pleasing peculiarity.

DRY SENSITIVES.

Hydrate of Lime.--The operation by which water is combined with lime is called slaking. Take a piece of quick lime, common lime used in mortar, and immerse it in warm water for about fifteen seconds; then place it in an iron or tin vessel.

It will soon begin to swell, evolving a great deal of heat and emitting steam, and soon falls into a fine powder, hydrate of lime.

This should be well stirred and allowed to cool, and then bottled in order to prevent it from giving off the hydrate and recovering the carbonic acid from the atmosphere.

The last is detrimental to its use with bromine, and is one cause of the complaint that "it will not take bromine."The hydrate of lime should, not be dried over a heat, as has been supposed by many, for in that case the hydrogen is expelled and it returns to a carbonate.

It is advisable to cool it in a damp place like a ground cellar.

Much of the lime in our market will not, except it be quite damp, combine with the bromine. This is owing to impurities.

Nothing is equal to oyster-shell lime, which I use altogether.

Bromide of Lime.--In preparing large quantities of this, we adopt the following method: Fill a four-quart bottle about two-thirds full of hydrate of lime; pour into this about one or two ounces of bromine;then shake well, add more of the bromine, shake well and let it stand for a few hours, adding sufficient bromine to give it a fine red color.

It is better when kept in the large bottles, as it forms a more perfect combination: in other words it improves by age.

Use.--Coat over the iodine to a rose red and then over this mixture to a purple or slate; recoat over the first about one fourth as long as first coating.

Gurneys American Compound.--Of this compound there are two combinations, one for use, when the temperature of the atmosphere is above 65 or 70deg., and the other at a lower temperature. The first is called No. 1, the second No. 2.