Arsenic trioxide

“ Arsenic burns on heating in a current of oxygen, with a pale lavender-coloured flame, forming the trioxide. It is easily oxidized by heating with concentrated nitric acid to arsenic acid, and with concentrated sulphuric acid to arsenic trioxide; dilute nitric acid only oxidizes it to arsenious acid. It burns in an atmosphere of chlorine forming the trichloride; it also combines directly with bromine and sulphur on heating, while on fusion with alkalis it forms arsenites. ”

“ The compounds of arsenic are very poisonous if taken into the system, and must be handled with care.
207. Separation. Experiment 115.—Draw out into two parts in the Bunsen flame a piece of glass tubing 20cm long and 1 or 2cm in diameter. Into the end of one of the ignition tubes thus formed, when it is cool, put one-fourth of a gram of arsenic trioxide, As2O3, using paper to transfer it. Now put into the tube a piece of charcoal, and press it down to within 2 or 3cm of the AS2O3 (Fig. 45) . Next heat the coal red-hot, and then at once heat the As203. ”

“ Arsenious oxide is very poisonous. It acts as a reducing agent; it is not convertible into the pentoxide by the direct action of oxygen; and its solution is reduced by many metals (e.g. zinc, tin and cadmium) with precipitation of arsenic and formation of arseniuretted hydrogen. The solution of arsenious oxide in water reacts acid towards litmus and contains tribasic arsenious acid, although on evaporation of the solution the trioxide is obtained and not the free acid. The salts of the acid are, however, very stable, and are known as arsenites. ”

“ Arsenic compounds can be detected in the dry way by heating in a tube with a mixture of sodium carbonate and charcoal when a deposit of black amorphous arsenic is produced on the cool part of the tube, or by conversion of the compound into the trioxide and heating with dry sodium acetate when the offensive odour of the extremely poisonous cacodyl oxide is produced. In the wet way, arsenious oxide and arsenites, acidified with hydrochloric acid, give a yellow precipitate of arsenic trisulphide on the addition of sulphuretted hydrogen ”

“ The Chemical Warfare Service developed the following method of preparation of the methyl derivative. Sodium arsenite (Na3AsO3) is prepared by dissolving arsenic trioxide in sodium hydroxide solution. The action of methyl sulfate at 850 C. gives [Pg 182] disodium methyl arsenite, Na2CH3AsO3. Sulfur dioxide reduces the arsenite to methyl arsine oxide, CH3AsO, which is then reacted with hydrochloric acid to give methyl dichloroarsine. The final product is distilled from the mixture and condensed. This material costs from two to two and a half dollars per pound for chemicals (war prices) . ”

“ Protect from light. d. Arsenic trioxide.* Dissolve 0.6602 g As 2O 3 in 5 mL 1 N NaOH. Dilute to 500 mL with deionized water. e. Arsenic pentoxide.* Dissolve 0.7669 g As 2O 5 in 5 mL 1 N NaOH. Dilute to 500 mL with deionized water. Calibration stock solution, 1 μg/mL mixed analyte. Dilute 0.1 mL of each stock standard (REAGENTS, 7.) with Eluent A in a 100-mL volumetric flask. Prepare fresh daily. ”

“ Background absorption is overcome by the use of a deuterium background corrector. Matrix modification with Ni 2+ solution allows the use of a higher char temperature in the graphite furnace. Other particulate arsenic compounds will interfere. ”

“ Method P&CAM 346 was developed in August, 1981, over the range 0.67 to 32.2 μg/m 3 for a 400-L air sample, corresponding to 0.268 to 12.8 μg As per sample [1] . Atmospheres were generated by passing air over heated As 2O 3. Collection efficiencies (CE) for As 2O 3 under these conditions were determined to be 0.42 and 0.67 for untreated 0.8-mm cellulose ester membrane filters, and cellulose backup pads, respectively. Under the same conditions, the Na 2CO 3-treated filter had CE = 0.93 [5] . ”

“ SPECIAL PRECAUTIONS: Arsenic is a carcinogen [6] . Handle appropriately. Perform all digestions in a fume hood.
SAMPLING: 1. 2.
Calibrate each personal sampling pump with a representative sampler in line. Sample at an accurately known flow rate between 1 and 3 L/min for a total sample size of 30 to 1000 L. Do not exceed a filter loading of ca. 2 mg total dust.
SAMPLE PREPARATION: 3. 4. 5.
Transfer both the treated filter and backup pad to a clean beaker. Add 15 mL conc. HNO 3 and cover with a watchglass. NOTE: Start reagent blanks at this step. ”

“ Another oxide likewise exists, which contains two equivalents of metal and five of oxygen, and, possessing strong acid properties, is denominated arsenic acid. The sesquioxide and arsenic acid unite with bases, and produce compounds which, with the exception of those they form with the alkalis, are mostly insoluble. Metallic arsenic unites with sulphur in two proportions, forming an orange-red and a sulphur-yellow compound. The compounds of arsenic have very little chemical action with vegetable and animal principles. ”

“ Arsenious acid also acts as an oxidizing agent, in that it gives up its oxygen to the protoxide of iron, converting it into the peroxide; but the arsenic itself, which has lost its oxygen, is reduced to the metallic state, and being volatile, does not remain with the glass, but passes off by the flues of the furnace. ”

“ The hydrogen comes off regularly even in the cold, but it is best to apply a little heat. This test will evolve arsine from arsenious acid, and also from arsenic trisulphide; but it is not available for the detection of arsenic, when the arsenic is in the form of arsenic acid. ”

“ It is a fine grayish-black powder, formed by exposing powdered arsenic for a long time to the air; but it also frequently contains fragments of the metal. It is usually considered by chemists to be a mixture of metallic arsenic and its white oxide.
It is acted on by water, the white oxide being found ere long in solution by its proper tests. Oxidation and solution, however, are also effected upon pure metallic arsenic in the same manner. A thousand grains of water take up a grain in the course of half an hour when boiled on the metal. ”

“ It is extremely delicate; for it will detect at least a 250,000th part of arsenic in solution; and it removes from the fluid every particle of arsenic, because none can be afterwards discovered by means even of Marsh’s method. It is not subject to any fallacy. The mere formation of a brilliant coating on the copper is not evidence of arsenic being present; for as Reinsch himself ascertained, solutions of bismuth, tin, zinc, and antimony produce a coating more or less similar to an arsenical one. ”

“ White arsenic is an oxide of arsenic, and is obtained by roasting arsenical ores, and refining the material (crude arsenic) , which condenses in the flues. Arsenic itself is volatile, and many of its compounds have the same property. It forms two well-defined series of salts, corresponding to the oxides: arsenious oxide (As2O3) , and arsenic oxide (As2O5) . These combine with bases to form arsenites and arsenates respectively. Boiling with nitric acid converts the lower into the higher oxide; and powerful reducing-agents, such as cuprous chloride, have the opposite effect. ”

“ It is necessary to observe in this place, that the arseniate, like the arsenite of potass, or that of ammonia, is obedient to the silver test, but that instead of the yellow precipitate which is produced by the latter salt, we obtain, by the former, a red or brick-coloured one.
If arsenious acid and quick-lime be heated together in a glass tube, a sudden ignition is occasioned at a certain temperature, when metallic arsenic will sublime, and an arseniate of lime be formed. In this case one portion of the arsenious acid is robbed of its oxygen to complete the acidification of the remainder. ”

“ Antimony minerals are very hard; the tersulphide is the most common, and from this the metallic antimony is produced. Red antimony, the oxide, is a rarer ore.
Arsenic resembles antimony, and occurs in combination with many metals. White arsenic, or arsenious acid, is found in Bohemia, Alsace, Transylvania, etc. Orpiment and realgar are sulphides of arsenic, and are employed as colouring matters in paint and fireworks. Arsenic is very poisonous. ”

“ A millionfold increase in concentration, even when we are dealing with very small numbers, would imply a millionfold increase in the activity of the solution. If, then, the oxidizing component of arsenic acid is the quinquivalent ion, As5+, which would tend to discharge two of its positive (oxidizing) charges, arsenic acid should be a much more powerful oxidizing agent in strong acid solution than in alkaline or neutral solutions. ”

“ And in particular they have been successfully employed to detect arsenic in those organs of the human body into which it can obtain admission only through the medium of absorption.
In the following statement I shall describe four processes only, that of Reinsch, by which the arsenic is first separated as a crust on copper,—that of Marsh, who first detaches it in the form of arseniuretted-hydrogen,—my own method, which consists in obtaining in the first instance a sulphuret of arsenic,—and that of Drs. Fresenius and von Babo, which has the same foundation. ”

“ When passed into a solution of silver nitrate it gives a blackish brown precipitate of metallic silver, the arsenic being oxidised. If acting on copper sulphate and similar salts, arseniuretted hydrogen sometimes forms arsenides—i.e. it reduces the metallic salt with its hydrogen, and is itself reduced to arsenic. Sulphuric, and even hydrochloric, acid reduces arseniuretted hydrogen to arsenic, and it is still more easily decomposed by arsenious chloride, and with phosphorous chloride it gives the compound PAs. ”

“ I do not think that arseniureted hydrogen could be formed under the conditions, for the oxygen compound of arsenic is in a state of combination, and the compound is in a dry solid state and not in solution and the affinities of the two elements—arsenic and hydrogen—for each other are so exceedingly weak that they cannot be made to unite directly except they are both set free at the same moment in presence of each other. ”

“ According to the theory, that arsenic acid is an oxidizing agent because it gives up oxygen of a definite pressure, this pressure would be the more effective, the more completely the opposing hydroxide-ion is suppressed by added acid (p. 280; see also p. 272, on the action of ferro-ion on silver-ion in the presence and in the absence of fluorides) . ”

“ In the ignition-tube a sort of metallic deposit appeared. Quickly he made one test after another. I sniffed. There was an unmistakable smell of garlic in the air.
"Arseniureted hydrogen," commented Craig. "This is the Marsh test for arsenic. That wall-paper in Brixton's den has been loaded down with arsenic, probably Paris green or Schweinfurth green, which is aceto-arsenite of copper. Every minute he is there he is breathing arseniureted hydrogen. Some one has contrived to introduce free hydrogen into the intake of his ventilator. ”

“ A similar result was obtained when an artificial mixture of 1 grm. of arsenious acid and 1 pound of earth were submitted to the same process.
The fact would appear to stand thus: oxide of iron in ordinary earth retains arsenic, and requires treatment with a concentrated acid to dissolve it. It therefore follows that, if a defence of arsenical earth is likely to be set up, and the analyst finds that by mere extraction of the tissues by water he can detect arsenic, the defence is in all probability unsound. ”

“ Arsenic may be detected by dissolving the substance in hydrochloric acid, or in aqua regia (avoiding an excess of nitric acid) , and adding a little of this solution to the contents of a small flask in which hydrogen is being made by the action of zinc and hydrochloric acid. The ignited jet of hydrogen assumes a blue colour if arsenic is present, and a cold porcelain dish held in the flame (fig. 67) becomes coated with a dark deposit of metallic arsenic. Antimony produces a similar effect, but is distinguished by the insolubility of its deposit in a cold solution of bleaching-powder. ”

“ Arsenious anhydride does not oxidise in air, either in a dry state or in solution, but in the presence of alkalis it absorbs oxygen from the air, and acts as an excellent reducing agent. This probably is connected with the fact that arsenic acid is much more energetic than arsenious acid, and that it is arsenic acid which is formed by the oxidation of the latter in the presence of alkalis. Arsenious anhydride is easily reduced to arsenic by many metals, even by copper. ”

“ If ignited gently in a stream of carbonic acid gas, the weight remains constant. To render it anhydrous, a heat of 200° is required.
The recognition of arsenic in the commercial sulphide is most easily effected by placing 2 grms. or more in a suitable retort (with condenser) , adding hydrochloric acid, and distilling. The chloride of arsenic passes over before the chloride of antimony; and by not raising the heat too high, very little antimony will come over, even if the distillation be carried almost to dryness. The arsenic is detected in the distillate by the ordinary methods. ”

“ Size is largely used for fixing colour; thus, the proper conditions for the development of arseniurretted hydrogen—the most dangerous compound of arsenic—are present. As much as 17 grains of arsenic have been discovered in each square foot of a wall-paper. Now, arsenic is sometimes given internally for certain skin and other diseases, but the dose is only from 1 ∕ 60 to 1 ∕ 12 grain; the capacity for poisoning of such a paper as the above will therefore be evident. ”

“ Proust and Thenard both found that 100 white oxide, when converted into acid by nitric acid, gave 115 or 116. I have found the same. Now if 116 ∶ 100 ∷ 156 ∶ 134; hence the white oxide of arsenic must contain 100 metal to 34 oxygen, if the data be correct; or the metal and oxygen are as 3 to 1 nearly. It is highly improbable that any inferior oxide subsists, as no traces of such have been found, if we disallow a conjecture of Berzelius on the subject. The white oxide of arsenic must then be considered as the protoxide, and the atom of arsenic must weigh 21 nearly, and that of the protoxide 28. ”