Potassium bichromate

“ Prepared by igniting potassium bichromate at a red heat and well washing the residue, and as hydrate by cautiously adding equal parts of hydrochloric acid and alcohol or sugar to a boiling solution of chromate of potassa in water, in small portions at a time, until the red tint disappears, and the liquid assumes a green colour; pure ammonia, in excess, is next added, and the precipitate which subsides is collected and washed with water. ”

“ When heated with phosphorus trichloride in a sealed tube to 160° C., potassium chlorochromate, phosphorus oxychloride, potassium chloride, and a complex chromium oxide (possibly Cr3O6) are produced (A. Michaelis, Jour. prak. Chem., 1871, ii. 4, p. 452) . Potassium bichromate finds application in photography, in calico-printing and in the preparation of bichromate cells. Sodium bichromate, Na2Cr2O7·2H2O, may be obtained by the addition of the requisite quantity of chromium trioxide to a solution of sodium chromate. ”

“ This close agreement between theory and observation led me to examine a case in which the specific resistances of the solutions were not the same, in order to see whether the method could be used when no solutions could be found with the exact resistance needed. I used potassium bichromate and potassium chloride, whose conductivities are and respectively. If the extension of method is practicable, these solutions should give the same velocity for the bichromate group as the former pair—bichromate and carbonate. The galvanometer was moved, and, therefore, had to be regraduated. ”

“ PROCEDURE.—Pulverize about 5 grams of potassium bichromate of good quality. Dissolve the bichromate in distilled water, transfer the solution to a liter bottle, and dilute to approximately 1000 cc. Shake thoroughly until the solution is uniform.
To prepare the solution of the reducing agent, pulverize about 28 grams of ferrous sulphate (FeSO_{4}.7H_{2}O) or about 40 grams of ferrous ammonium sulphate (FeSO_{4}. (NH_{4}) {2}SO{4}.6H_{2}O) and dissolve in distilled water containing 5 cc. of concentrated sulphuric acid. Transfer the solution to a liter bottle, add 5 cc. ”

“ The commercial salt is very impure. Purchase that sold as potassic cyanide (gold) which contains about 95 per cent. of KCN. It is used for copper assaying and occasionally in separation. Make a 10 per cent. solution when wanted.
Potassium Bichromate, K2Cr2O7. It may be purchased nearly pure. It is used as an oxidising agent, for determining iron; and as a test solution. For this last purpose a 10 per cent. solution is prepared.
Potassium Chlorate (KClO3) can be purchased pure. It is used with hydrochloric acid as a substitute for aqua regia. ”

“ Two salts are in common use for this purpose, potassium permanganate and potassium bichromate. It is necessary in the first place, after the ore is in solution, to reduce all the iron to the ferrous condition; then the carefully standardized solution of the oxidizing reagent is added until all the iron is in the ferric state, the volume of the standard solution used being the measure of the iron contained in the ore. The end of the reaction when potassium permanganate is employed is known by the change in colour of the solution. ”

“ The “two bath process” consists of treating the skins with a bichromate in which the chromium is in the acidic state, and afterwards reducing it to the basic state by some reducing agent. The exact process is as follows: To prevent wrinkled or “drawn” grain the goods are first paddled for half an hour in a solution of vitriol and salt, when they are piled or “horsed” up over night, and then, without washing, placed in a solution consisting of 7 ℔ of potassium bichromate, 31/2 ℔ of hydrochloric acid to each 100 ℔ of pelts, with sufficient water to conveniently paddle in ”

“ Heat gently for a few minutes, and then boil until the nitric oxide is expelled. An atmosphere of carbon dioxide must be kept up. Dilute with water, and titrate the residual iron with standard solution of bichromate of potassium. The standard "bichromate" is made by dissolving 17.5 grams of the salt (K2Cr2O7) in water, and diluting to 1 litre: 100 c.c. equal 2 grams of iron. Deduct the weight of iron found from the 2 grams originally taken, and multiply by 0.3214. This gives the weight of the pentoxide in the sample. In an example, 0.5 gram of nitre was taken, and 59.4 c.c. ”

“ Very strong: A boiling solution of potassium chlorate, 30 parts, in water, 300 parts, poured into a mixture of pure hydrochloric acid, 300 parts; water, 300 parts.
For etching on copper a saturated solution of bromine in dilute hydrochloric acid may also be used; or a mixture of potassium bichromate, 1/2 part; water, 1 part; crude nitric acid, 3 parts. ”

“ It is ground and stirred up with hot water, and sulphuric acid is added till a slight acid reaction becomes apparent, a sign that the neutral chromate has been converted into bichromate. Chalk is now stirred in to precipitate the ferric sulphate, and after a while the clear solution is run off into another vessel, where it is treated with carbonate of potassium, which precipitates the lime and leaves bichromate of potassium in solution. The solution is then evaporated to the crystallising point. This process, when carried out on a large scale, is very economical. ”

“ Bichromate of ammonium, the crystals of which somewhat resemble those of the potassium salt. In colour they are of a browner hue, and readily51 distinguishable, since when heated on platinum deflagrates, emitting sparks and leaving a residuum of very finely-divided oxide of chromium. The ammonium salt does not, however, so readily crystallise on account of its considerably greater solubility in water compared with bichromate of potassium. ”

“ Chromate and bichromate of potassium give yellow precipitates insoluble in dilute nitric acid, and soluble in solution of potassium hydrate. Iodide of potassium gives a yellow precipitate, soluble in great excess by heat, and separating in small, brilliant, golden-yellow scales, as the liquid cools. A piece of polished zinc precipitates metallic lead in an arborescent form, hence called the lead tree. To prepare for these tests, a solid supposed to contain lead should be digested in nitric acid, when the solution, evaporated to dryness and redissolved in water, may be tested as above. ”

“ After the calcium sulphate has settled, the potassium chromate solution is converted into bichromate by the action of sulphuric acid, and the salt is allowed to crystallize. It forms large triclinic prisms of specific gravity 2.6-2.7, which are moderately soluble in cold water and readily soluble in hot water. ”

“ The carbon tissue of commerce is not sold in a sensitive condition; therefore, the first care will be to render it sensitive to the action of light, which is done by immersion in a solution of bichromates of potash and ammonia.
First of all dissolve in eighty ounces of water one and a half ounces of bichromate of ammonia, and one ounce of bichromate of potassium, and filter. Then cut the carbon tissue into suitable sized pieces—i. ”

“ At 32° F. it is brittle, like glass; at 59° it is soft and malleable; at 144° it becomes liquid. Potassium is widely diffused in the vegetable, animal and mineral kingdoms. Some of the more important potassium compounds are caustic potash (the hydroxide) , the carbonate, the bicarbonate; also potassium chloride, bromide, iodide, nitrate (saltpeter) , sulphate, chlorate, cyanide etc. Of these iodide, bromide and chlorate are used for medicines, the others being employed more or less in the arts. ”

“ Those elements which unite with the utmost eagerness at ordinary temperatures, seem to become indifferent 272to each other when subjected to the extremes of heat and cold. Potassium unites fiercely with oxygen in the most familiar of all chemical experiments. Potassium is indeed a strange metal, for it is of such small density that a piece cast on a basin of water will float like a chip of wood. It has such avidity for oxygen that it will decompose the water to wrench the molecules of oxygen from those of hydrogen. ”

“ Bichromates.—The bichromates are usually of a red or reddish-brown colour, those of the alkali metals being readily soluble in water. They are readily decomposed by heat, leaving a residue of the normal chromate and chromium sesquioxide, and liberating oxygen; ammonium bichromate, however, is completely decomposed into chromium sesquioxide, water and nitrogen. Sulphuretted hydrogen and sulphur dioxide reduce them in acid solution to the condition of chromium salts. ”

“ In 1807, Sir Humphry Davy discovered the metal potassium by subjecting moistened potash to the action of a powerful voltaic battery; the positive pole gave off oxygen and the metallic globules of pure potassium appeared at the negative pole. It is never found uncombined in nature. Now if potassium is heated in cyanogen gas (a gas procured by heating mercury) or obtained on a large scale by the decomposition of yellow prussiate of potash, a white crystalline body very soluble in water, and exceedingly poisonous, is obtained. ”

“ Potassium, Bicarbonate of. KHCO3. Syn. Potassium hydrogen carbonate, Bicarbonate of potassa; Potassæ bicarbonas (B. P., Ph. L., E., & D.) . Prep. 1. (Ph. L. 1836.) Carbonate of potassium, 6 lbs.; distilled water, 1 gall.; dissolve, and pass carbonic anhydride (from chalk and sulphuric acid diluted with water) through the solution to saturation; apply a gentle heat, so that whatever crystals have been formed may be dissolved, and set aside the solution that crystals may again form; lastly, the liquid being poured off, dry them. ”

“ Carbonic ether, Carbonate of oxide of ethyl; Æther carbonicus, L. Prep. Fragments of potassium are added to oxalic ether, gently warmed, as long as bubbles of gas are formed; the excess of metal is removed from the semi-solid mass, some water added, and the whole distilled. The carbonic ether floats on the surface of the liquid in the receiver, and is collected, dried by contact with chloride of calcium, and rectified along with some potassium or sodium, till it ceases to yield acetate of potassa when acted on by caustic potassa. ”

“ Salts are formed when a “basis,” i.e., a metal oxide, replaces water. When potassium-acid sulfate is neutralized by sodium base, the acid-salt divides into Glauber’s salt and potassium sulfate, which proves the acid-salt to be a mixture of the neutral salt with its acid. Sodium-acid phosphate behaves quite differently. After neutralization by a potassium “base” (hydroxide) , the salt does not split up; a uniform sodium-potassium phosphate is obtained. Therefore, phosphoric acid is truly three-basic! ”

“ The paper will be found covered with a solution of ordinary potash. If turmeric paper be used, the course of the potassium will be marked with a deep brown color.—Corollary. Hence, if you touch potassium with wet fingers you will burn them.
If a small piece of the metal be placed on a piece of ice, it will instantly take fire, and form a deep hole, which will be found to contain a solution of potash.
In consequence of its great affinity for oxygen, potassium must be kept in some fluid destitute of that element, such as naphtha. ”

“ Plates should always be kept in a dry room. The dark room is seldom a safe place for storage, because it is apt to be damp.
Various developing agents give different results. Pyrogallic acid in combination with carbonate of sodium or carbonate of potassium gives strong, vigorous negatives. Eikonogen and metol yield soft, delicate negatives. Hydrochinon added to eikonogen or metol produces more contrast or greater strength.
It is essential to have a bottle of bromide of potassium solution, 10 per cent, in the dark room. (One ounce of bromide of potassium, water to 10 ounces.) ”

“ Fourthly, by mixing together various earths with the oxides of tin, iron, lead, silver, and mercury: a mode of manipulation suggested by the results of his previous experiments 299 on potassium, in which he found that when a mixture of potash and the oxides of mercury, tin, or lead, was electrified in the Voltaic circuit, the decomposition was very rapid, and an amalgam, or an alloy of potassium, was obtained; the attraction between the common metals and the potassium apparently accelerating the separation of the oxygen. ”

“ It requires more than 1200 parts of water for its solution: for its perfect purification, it should be heated with a solution of chloride of potassium, the insoluble portion separated whilst the liquid is lost, and the peculiar salt allowed to deposit as the temperature falls. When heated, it behaves like the salt of silver. ”

“ It is used in testing for metallic oxides and silica before the blowpipe. The crystals are sometimes used as a standard for phosphoric acid.
"Nessler's Solution."—Mode of preparation: Dissolve 35 grams of potassium iodide in 100 c.c. of water; dissolve 17 grams of mercuric chloride in 300 c.c. of water, and pour this solution into that of the iodide till a permanent precipitate is produced; make up to 1 litre with a 20 per cent. solution of potash; add mercuric chloride till a precipitate is again formed; allow to settle and decant. It is used for detecting ammonia. ”

“ This shows that the molecule of potassium (like that of sodium, mercury, and zinc) contains but one atom. This is also the case with many other metals, judging by recent researches. [19] The specific gravity of potassium at 15° is 0·87, and is therefore less than that of sodium, as is also the case with all its compounds. [20] Potassium decomposes water with great ease at the ordinary temperature, evolving 45,000 heat units per atomic weight in grams. The heat evolved is sufficient to inflame the hydrogen, the flame being coloured violet from the presence of particles of potassium. ”