Picric acid

“ Picric acid, the nature of which we have several times previously mentioned, and which explodes at 600° F. (only 28° above gunpowder) , may also be an element in such explosions during fires. Its salts form, in combinations, various powerful explosives, much exceeding gunpowder in force; and they have been used to a considerable extent in Europe. Picric acid, now much employed by manufacturers and dyers for obtaining a yellow color, is always kept in store largely by drysalters and druggists, and generally by dyers, but in smaller quantity. ”

“ If the ether extract contains much impurity, it may be necessary to drive off the ether, and to take up the residue with a little warm water, then to cool, filter through a moistened filter paper, and test the aqueous solution. Picric acid, warmed with KCN and KHO gives a blood-red colour, from the production of iso-purpurate of potash. Ammoniacal copper sulphate forms with picric acid yellow-green crystals which strongly refract the light. ”

“ Another method which may be used for the separation and purification of neuridine is to dissolve it in alcohol and precipitate with an alcoholic solution of picric acid; the picrate may be decomposed by treatment with dilute mineral acid, and the picric acid removed by shaking with ether.
The free base has a strong seminal odour. It is gelatinous, and has not been crystallised. It is insoluble in ether and in absolute alcohol, and not readily soluble in amyl alcohol. It gives white precipitates with mercuric chloride, neutral and basic lead acetates. ”

“ Picrates are more often used than picric acid itself in powders. One of the best known is Brugère's Powder, which is a mixture of 54 parts of picrate of ammonia and 45 parts of saltpetre. It is stable and safe to manufacture. It has been used in the Chassepôt rifle with good results, gives little smoke, and a small residue only of carbonate of potash. ”

“ When the temperature is raised, a point (K) is reached at which the compound melts with separation of solid picric acid. The point, K, is, therefore, a transition point; analysis, however, showed that the composition of the solution at this point is very nearly that of the compound C6H2 (NO2) 3OH,C6H6, so that the melting point of the compound can almost be reached. The fusion of the compound of benzene and picric acid with separation of the latter is analogous to the (partial) fusion of Glauber's salt with separation of anhydrous sodium sulphate. ”

“ Local Action.—When strong nitric acid comes in contact with organic matters, there is almost constantly a development of gas. The tissue is first bleached, and then becomes of a more or less intense yellow colour. Nitric acid spots on the skin are not removed by ammonia, but become of an orange-red when moistened with potash and a solution of cyanide of potassium. The yellow colour seems to show that picric acid is one of the constant products of the reaction; sulphide of ammonium forms a sort of soap with the epidermis thus attacked, and detaches it. ”

“ Dissolve the yellow resin of Xanthorrhœa hastilis (Botany Bay Gum) in a sufficiency of strong nitric acid. Red vapours are evolved, accompanied by violent frothing, and a deep red solution is produced, which turns yellow after boiling. Evaporate this solution over a water bath. A yellow crystalline mass is deposited, which consists of picric acid with small quantities of oxalic and nitrobenzoic acids. The picric acid is purified by neutralising the yellow mass with potassa, and crystallising twice out of water. ”

“ Picric acid has the bad habit of attacking the metals with which it rests in contact forming sensitive picrates that are easily set off, but TNT is inert toward metals and keeps well. TNT melts far below the boiling point of water so can be readily liquefied and poured into shells. ”

“ A solution of calcium picrate, that is, the lime salt of picric acid, is pumped in and as the reaction begins the mixture heats up and the chlorpicrin distils over with the steam. When the distillate is condensed the chlorpicrin, being the heavier liquid, settles out under the layer of water and may be drawn off to fill the shell.
[Pg 227] Much of what a student learns in the chemical laboratory he is apt to forget in later life if he does not follow it up. But there are two gases that he always remembers, chlorine and hydrogen sulfide. ”

“ To a third portion, a little ammonium sulphide, containing free ammonium hydroxide, is added; in presence of picric acid, picramic acid is produced, the formation of which is accelerated by the application of heat, and is made evident by the appearance of an intensely red colour.
The detection of cocculus indicus, or its poisonous alkaloid, picrotoxine, may be effected by first agitating the beer with plumbic acetate, filtering, removing the lead from the filtrate by means of sulphuretted hydrogen, and again filtering. ”

“ It precipitates lead acetate but not lead nitrate, while tannin precipitates both. A dilute solution of potassium cyanide gives a red coloration which disappears on standing, but is restored by shaking with air. If to even a very dilute solution of gallic acid, sodic arsenate, or some other faintly alkaline salts be added, the mixture absorbs oxygen and becomes a deep green. Aqueous solution of picric acid to which excess of ammonia has previously been added gives a red coloration, changing to green. ”

“ The precipitate contains the picrate of trimethylenediamine, mixed with the picrates of cadaverine and creatinine. Cadaverine picrate is insoluble in boiling absolute alcohol, the other picrates soluble; so the mixed picrates are boiled with absolute alcohol, and the insoluble cadaverine filtered off. Next, the picrates of creatinine and trimethylenediamine are freed from alcohol, the solution in water acidified with hydrochloric acid, the picric acid shaken out by treatment with ether, and then the solution precipitated with platinum chloride ”

“ Its aqueous solution gives a white precipitate with both normal and basic lead acetate, which when heated, acquires first a rose, and then a chocolate colour; with ferric chloride a green liquid is produced, which changes after a time to red and becomes black on addition of sodium acetate. It forms white precipitates with gelatin, albumen, and alkaloids. By dry distillation it yields catechol. By fusion with potash or the action of sulphuric acid, phloroglucol and protocatechuic acid, while nitric acid converts it into oxalic and picric acids. ”

“ Sulphuric acid and sugar gives a different colour to that produced by commercial veratrine. There is first a green colour which darkens into olive green, then becomes dirty green, and finally dark brown. When warmed with strong sulphuric, hydrochloric, or phosphoric acids, there is a strong odour of isobutyric [392] acid developed. Dilute solutions of the salts are precipitated by ammonia, Nessler’s reagent, gold chloride, potassium mercury iodide, cadmium iodide, phosphotungstic acid, and picric acid; no precipitate is produced by tannin, platinum chloride, or mercuric chloride. ”

“ When aloine is digested for some time with strong nitric acid, much nitrous gas is evolved, and it is converted into chrysammic acid, but without the formation of any nitro-picric acid, as is always the case when crude aloes is subjected to a similar treatment. A quantity of aloine was boiled with a mixture of chlorate of potash and muriatic acid. The acid solution was evaporated to dryness, and digested with strong spirits of wine. ”

“ Marchi’s fluid is used especially for the study of nerve-degeneration, and Altmann’s for the demonstration of Altmann’s granules. The method of Pianese is used for the demonstration of cell-inclusions. The osmic-acid mixtures are all expensive, penetrate poorly, cause precipitates, and affect greatly the staining-power of the tissues, so [Pg 231] that it becomes necessary to use certain stains (safranin, carbol fuchsin, aniline gentian violet, etc.) as counterstains.
8. PICRIC ACID. A saturated water solution of picric acid is usually employed. ”

“ If the burning liquid be poured out upon a cold slab, it will soon go out. A small quantity carefully heated in a tube, closed at one end, can even be completely volatilised without apparent decomposition. It is thus obvious that picric acid is much less explosive than the nitric ethers, such as nitro-glycerol and nitro-cellulose, and very considerably less explosive than the nitrogen compounds and fulminates. ”

“ If pure materials only are used, the manufacture presents no danger. The finished material, however, must be carefully kept from contact with nitrates, chlorates, or oxides. If only a little bit of lime or plaster become accidentally mixed with it, it may become highly dangerous. A local explosion may occur which might have the effect of causing the explosion of the whole mass. Picric acid can be fired by a detonator, 5-grain fulminate, and M. Turpin patented the use of picric acid, unmixed with any other substance, in 1885. ”

“ It may also be made from benzene without converting it into phenol thus: The benzene is chlorinated and gives chlorbenzene. This is nitrated into dinitrochlorbenzene, and is then treated with caustic soda to give dinitrophenol. This is then further nitrated into trinitrophenol or picric acid. Picric acid has a high melting-point, it must be used pure, is dissolved by water, it attacks metals [414] forming dangerous compounds, and requires troublesome plant for its manufacture. ”

“ In two specific cases men have talked of having contracts for picric acid—the manufacture of which necessitates the most skilled training, with most expensive and complicated machinery, and which is only being attempted in four places in this country, and were promptly paid off, on their pledge that they would violate these alleged agreements. ”

“ It is almost insoluble in alcohol, chloroform, methyl alcohol, and acetone, and insoluble in benzene, light petroleum, and ether. Concentrated sulphuric acid gives a violet, then a cherry-red colour. Its solution in concentrated hydrochloric acid becomes light red on warming, and there is an odour of isobutyric acid. It is readily soluble in dilute mineral acids, and the solution, on the addition of ammonia, yields the alkaloid in a crystalline condition. The sulphuric acid solution gives precipitates with phosphotungstic, picric, and tannic acids, and with potassium mercury iodide ”

“ They are nearly all highly soluble in alcohol. Æther readily dissolves Delphia, Veratria, Emeta, Quina, and Gentia; but Morphia, Cinchonia, and Picrotoxa, are very sparingly soluble: and Strychnia and Brucia are nearly insoluble in it; they combine with the acids; and, in general, form neutral salts; but it appears that Veratria and Emeta always unite with an excess of acid. All the combinations with the mineral acids, excepting the salts of Picrotoxa, are exceedingly soluble in water; and, with the exception of Nitrate of Cinchonia, and all the salts of Veratria, they are crystallizable. ”

“ When a large excess of benzoic chloride is employed, no definite product is obtained.
Acetylpikrotin, C15H17O7Ac, crystallises from benzene, alcohol, or acetic acid in glistening plates melting at 244-245°, and is probably identical with the compound described by Paternò and Oglialoro as diacetylpikrotoxinin and melting at 227°. When pikrotin is allowed to remain in contact with acetic chloride for 24 hours at the ordinary temperature, and then heated until complete solution ensues, two compounds are obtained. ”

“ It crystallizes in small quadrilateral prisms, white and transparent, or in needles grouped in stars. No odor, taste bitter, insoluble in water, partly soluble in alcohol and in ether, freely soluble in acids and alkalies. A solution in concentrated sulphuric acid has a saffron-yellow color. Nitric acid transforms it into oxalic acid. [25]
Picrotoxinin exists in picrotoxin in the proportion of 32 to 100, and may be separated by boiling in benzine. It is bitter, poisonous, reduced by Fehling’s solution and nitrate of silver. Sixty-six per cent. ”

“ Pectic acid, though it rarely exists ready-formed in the plant, can readily be obtained from it by the action of weak alkalis. It is best procured by boiling the pulp of turnips with a 10 per cent. solution of sodium carbonate for about half an hour. If an acid be added to the filtered liquid, pectic acid is precipitated as a transparent colourless jelly, which {29} dries up to a transparent horny mass. By the prolonged action of alkalis or acids, pectic acid is converted into metapectic acid (C8H14O9) , which may be obtained as a syrupy, strongly acid liquid. ”

“ There are moreover certain neutral acrid principles, similar in their nature to resins, which are soluble only in alkalies, and thus come under this head. Such are Cantharidin, Piperin, Pyrethrin, Colocynthin, Elaterin, and Capsicin, obtained from Cantharides, Pepper, Pyrethrum, Colocynth, Elaterium, and Capsicum. But it should be observed that some of these are soluble in Acetic acid; and if, as some have supposed, this acid exist in the gastric juice, then they might be dissolved in the stomach. ”

“ Piperic acid differs from piperonylic acid by the group C4H4, and it was apparent that these carbon atoms must be attached to the carbon atom which appears in the carboxyl group of piperonylic acid, for if they were directly attached to the benzene ring polycarboxylic acids would result in oxidation. ”

“ Châteaubriand sauce is by no means acid; there must be only a just perceptible dash of acidity, and only so much lemon juice used as will give it zest. Piquante sauce is different; there should be acidity enough to provoke appetite; yet even this should be by no means sour.
To make Piquante sauce, chop a shallot fine, put it, with a tablespoonful of vinegar, [36] into a very small saucepan; let them stew together until the vinegar is entirely absorbed, but do not let it burn. Then add to it half a pint of Spanish sauce and a gill of stock, with a bay-leaf and a sprig of thyme ”