Hydrocyanic acid tests

There is a discrepancy between the cyanide criteria for both aquatic and drinking water standards and the current analytical technology. The criteria are stated for free cyanide (which Includes hydrocyanic acid and the cyanide ion), but the EPA approved analytical methodology for total cyanide measures the free and combined forms (11). This test probably overestimates the potential toxicity. An alternative method (cyanides amenable to chlorination) measures those cyanide complexes which are readily dissociated, but does not measure the iron cyanide complexes which dissociate in sunlight. This method probably tends to underestimate the potential toxicity. Other methods have been proposed, but similar problems exist (12). The Department of Ecology used the EPA-approved APHA procedure which includes a distillation step for the quantification of total cyanide (13,14). A modification of the procedure which omits the distillation step was used for estimation of free cyanide. Later in the study, the Company used a microdiffusion method for free cyanide (15). 

While still moist the bulk of the material is transferred to a test tube even in the moist condition pressing with a metal spatula or other hard object is to be avoided. Then 2 c.c. of concentrated hydrochloric acid are poured into the test tube, when the odour of free fulminic acid can be perceived. This odour so closely resembles that of hydrocyanic acid as to make confusion possible. After half an hour the contents of the test tube are heated for a short time in the boiling water bath, 4 c.c. of water are added, silver chloride is removed by filtration, and the filtrate is evaporated to dryness on... 

Many of the early gases used in artillery shell proved unsuitable or were not adapted to field conditions. Thus, out. of more than 50 chem substances loaded into artillery shell, oaly 4 or 5 proved effective in battle. Often the efficiency of a shell could be definitely. ascertained only after a large number of rounds had been fired. For example, the French Vincennite shell was filled with a raixt of hydrocyanic acid arsenic trichloride, which had a marked toxicity in lab tests. Yet, after 4 million shells were filled with this mixt it was not an effective gas under battle conditions... 

The liberation of hydrocyanic acid due to complete hydrolysis of cyano-genic glycosides can be determined by a simple colour test using sodium picrate paper (yellow), which turns red (sodium isopurpurate) in contact with HCN. 

The discovery of Liebig, that when hydrocyanic acid was mixed with sulphide of ammonium, and subjected to a moderate degree of heat, a compound— snlphocyanide of ammonium—was formed, which possessed the property of giving an intense blood-red color with the sesquisalts of iron, afforded a test for hydrocyanic acid, which is equal, if not superior, to any at present known, Dr, Pereira remarks —When the acid is in small quantity, and mixed with solids or... 

Heat amygdalin with dilute sulphuric acid under reflux for a short time. Remove benzaldehyde and hydrocyanic acid by steam distillation. Test for benzaldehyde (phenylhydrazone test) and hydrocyanic acid (Prussian blue test) in distillate, and for glucose (osazone test) in residue. 

Initial preparative work with oxynitrilases in neutral aqueous solution [517, 518] was hampered by the fact that under these reaction conditions the enzymatic addition has to compete with a spontaneous chemical reaction which limits enantioselectivity. Major improvements in optical purity of cyanohydrins were achieved by conducting the addition under acidic conditions to suppress the uncatalyzed side reaction [519], or by switching to a water immiscible organic solvent as the reaction medium [520], preferably diisopropyl ether. For the latter case, the enzymes are readily immobilized by physical adsorption onto cellulose. A continuous process has been developed for chiral cyanohydrin synthesis using an enzyme membrane reactor [61]. Acetone cyanhydrin can replace the highly toxic hydrocyanic acid as the cyanide source [521], Inexpensive defatted almond meal has been found to be a convenient substitute for the purified (R)-oxynitrilase without sacrificing enantioselectivity [522-524], Similarly, lyophilized and powered Sorghum bicolor shoots have been successfully tested as an alternative source for the purified (S)-oxynitrilase [525],... 

This consists essentially of sugar and almond paste. Besides the determination of the sugars, which is made as in biscuits, and the microscopic examination for the detection of other seeds and extraneous flours, tests for hydrocyanic acid (from the bitter almonds) and nitrobenzene (added as an adulterant) are also necessary. 

Test for Hydrocyanic Acid.—2 5 grams of the substance are digested for an hour with 30 c.c. of water and a few drops of potassium hydroxide solution, the liquid being then rendered add with sulphuric add and distilled, the first 3 c.c. of distillate being collected and tested by means of the Prussian blue reaction, which is carried out as follows ... 

The tests to be made on spirits and liqueurs include a certain number which are common to all these products, such as determinations of the alcoholic strength, extract and ash, and tests for impurities and denaturing agents other investigations are made only with certain products, examples of these being the examination of kirschwasser for hydrocyanic acid, the determination of sugars in liqueurs, etc. The former are treated under General Methods and the latter in the Special Part. 

The methods of analysis are those used for other spirits in addition, for nut-fruit spirits, hydrocyanic acid and benzaldehyde and sometimes nitrobenzene are tested for and determined as follows ... 

A) Qualitative Test, (a) Free hydrocyanic acid. About 5 c.c. of the liquid are shaken in a test-tube with a few drops of fresh alcoholic... 

The above methods cannot be used if the spirit contains chlorides, as may happen if it has been broken down with water containing these salts. In this case the total hydrocyanic acid may be determined by distilling 100 c.c. of the spirit and collecting at least three-quarters (which will contain all the hydrocyanic acid present) in a dilute solution of silver nitrate of known titre. The liquid is then made up to a definite volume and filtered, the excess of silver in an aliquot part of the filtrate being titrated with thiocyanate as already described. The free hydrocyanic acid, in presence of chlorides, should be determined colorimetrically as follows a solution of about 0-05 gram of potassium cyanide per litre is prepared and its exact content of HCN determined by titration with silver nitrate and ammonium thiocyanate. In a series of test-tubes are placed such quantities of this... 

Hydrocyanic Acid Transfer 1 mL of sample into a test tube. Add 1 mL of water, 5 drops of a 1 10 solution of sodium hydroxide, and 5 drops of a 1 10 solution of ferrous sulfate. Shake thoroughly, and acidify with 0.5 N hydrochloric acid. No blue precipitate or color appears. 

Dilute hydrochloric acid hydrocyanic acid, HCN, with an odour reminiscent of bitter almonds, is evolved in the cold. It should be smelled with great caution. A more satisfactory method for identifying hydrocyanic acid consists in converting it into ammonium thiocyanate by allowing the vapour to come into contact with a little ammonium polysulphide on filter paper. The paper may be conveniently placed over the test-tube or dish in which the substance is being treated with the dilute acid. Upon adding a drop of iron(III) chloride solution and a drop of dilute hydrochloric acid to the filter paper, the characteristic red colouration, due to the iron(III) thiocyanate complex, Fe(SCN)3, is obtained (see reaction 6 below). Mercury(II) cyanide is not decomposed by dilute acids. 

Alternatively, place a drop of the test solution (or a few milligrams of the test solid) in the reaction bulb of Fig. 11.56, add 2 thin pieces zinc foil and 2-3 drops dilute sulphuric acid. Place a small circle of quantitative filter paper (or drop-reaction paper) moistened with acetate-benzidine acetate reagent across the funnel. The paper is coloured blue by the hydrocyanic acid carried over with the hydrogen. 

H Acid Solution. 1 per cent in 5 per cent soda, is used to test for easily coupling diazo compounds in spot tests on filter paper. R salt, y3-naphthol, hydrocyanic acid, etc. can also be used for this purpose. 

When soluble cyanides or ferro and ferri-cyanides are distilled in the presence of potassium chlorate, with sulphuric acid, free hydro cyanic acid is found in the dislillatc insoluble substances of this nature, such as Prussian and Turnbull s blue, and the spent oxide of gasworks also are decomposed. Acoordingly, when testing for cyanogen compounds, l g. of the scraped match-heads is treated with so c.c. of warm water and filtered, and both the filtrate and the residue distilled separately with dilute sulphuric add. Hydrocyanic acid can be identified in the disttUate by the following reactions... 

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