According to one method, the film is sensitized with potassium dichromate and exposed to light under a reversed negative.
After the dichromate has been washed out, the film is soaked in glycerin and water.
Give the action of sulphuric acid on potassium dichromate (a) in the presence of a large amount of water; (b) in the presence of a small amount of water.
Since the chromate changes into a dichromate in the presence of an acid, it will be sufficient to study the action of the dichromates alone.
The dichromate decomposes in very much the same way as a permanganate does, the potassium and chromium being both changed into salts in which they play the part of metals, while part of the oxygen of the dichromate is liberated.
The platinum wires extending into the tubes B and D are now connected with the wires leading from two or three dichromate cells joined in series.
The reason why the potassium salt rather than the sodium compound is used is that sodium chromate and dichromate are so soluble that it is hard to prepare them pure.
It will be noticed that the oxidizing action of potassium dichromate leaves potassium sulphate and chromium sulphate as the products of the reaction.
When a dilute solution of a chromate or dichromate is acidified with an acid, such as sulphuric acid, no reaction apparently takes place.
On evaporating the solution these substances crystallize out as potassium chrome alum, which substance is produced as a by-product in the industries using potassium dichromate for oxidizing purposes.
Potassium dichromate finds use in many industries as an oxidizing agent, especially in the preparation of organic substances, such as the dye alizarin, and in the construction of several varieties of electric batteries.
The first of these disinfectants is stated to be a mixture of the sulphates of copper and aluminium, with potassic dichromate and turpentine.
Distilled with dichromate of potassium and sulphuric acid it is converted into benzoic acid.
It is then oxidized to anthraquinone by means of sodium dichromate and sulphuric acid in leaden vats, steam heated so that the mixture can be brought to the boil.
The aldehydes may be prepared by the careful oxidation of primary alcohols with a mixture of potassium dichromate and sulphuric acid,--3R.
Another patent, taken out in 1879 by Heinzerling, specified the use of potassium dichromate and alum.
Into this type fall also the liquors formed by passing sulphur dioxide gas into dichromate solution.
The dichromate is first dissolved, and the acid added gradually.
In this the tanning liquor was made by reducing potassium dichromate in the presence of a limited amount of hydrochloric or sulphuric acid by adding glucose.
A patent was taken out later by Cavallin in which skins were to be tanned by treating with potassium dichromate and then with ferrous sulphate which reduced the former to chromic salts, being itself converted into ferric salt.
The amount of hypo necessary is almost directly proportional to the amount of dichromate used.
The alum had its own tanning action and the dichromate was reduced to chromic salts by the organic matter of the skin itself and by the greases employed in dressing.
Gelatine is used in the numerous carbon processes, in which the principle is that gelatine is made insoluble in water by the action of potassium dichromate under the action of light.
Of the third type the most common is that in which the dichromate is reduced by sulphuric acid and sodium bisulphite.
The goods are chromed by a one-bath liquor containing dichromate (say 2 per cent.
In chroming with baths of the acid or neutral type, the percentage of hypo should be about three times the percentage of dichromate used.
Chromate and dichromateof potassium give no precipitate with neutral salts of brucine; on the other hand, strychnine chromate is at once formed if present.
Potassium dichromate gives no immediate precipitate, but crystals form on long standing.
The following group reagents precipitate narceine:--picric acid, tannin solution, and potassium dichromate on long standing.
The paper is prepared by floating it on a bath of aqueous solution of potassium dichromate and a trace of phosphoric acid, and then drying it in the dark.
It is based on the fact that an acid in the presence of potassium dichromate strikes a blackish-green color when brought in contact with aniline.
Technical sodiumdichromate generally contains a certain amount of chlorides, and the chlorine liberated from these tends to cause a troublesome foam towards the end, of the reaction.
As soon as this color remains permanent (a slight excess of sodium dichromate does no harm) the reaction is complete.
At first a greenish-black precipitate forms, but upon further addition of the sodium dichromate solution, the color changes to yellowish green.
The amount of solid sodium dichromate given is for the dry crystalline compound containing two molecules of water of crystallization.
When technical sodium dichromate is used, the solution should be filtered with suction, before it is added to the hydroquinone, in order to remove any insoluble impurities.
It is essential that the stirring should be most efficient, so that when the mixture becomes thick the dichromate will be evenly distributed throughout the liquid, as rapidly as it is added.
Commercial sodium dichromateis hygroscopic and contains varying amounts of water.
Other Methods of Preparation Quinone may be prepared by the oxidation of aniline with dichromate or manganese dioxide and sulfuric acid.
After this it is well washed to remove the unaltered gum and dichromate salt.
This is performed in a solution of potassium dichromate rendered alkaline with ammonia.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "dichromate" in a variety of sentences. We hope that you will now be able to make sentences using this word.
