Chapter VII: Analysis of Explosives (2)

The same chemists (_Compt. Rendus_, lxxxiii. 707) also devised the following method for determining the NO_{2} in nitro-glycerine:--A known quantity of a solution of ferrous sulphate of previously ascertained reducing power is placed in a flask, acidified with hydrochloric acid, and its surface covered with a layer of petroleum oil. About .5 grm. of the nitro-glycerine is then introduced, and the flask heated on the water bath. When the sample is completely decomposed, the liquid is heated to boiling to remove nitric oxide, and the excess of ferrous sulphate ascertained by titration with standard permanganate; 56 of iron (Fe) oxidised by the sample correspond to 23 of NO_{2} in the sample of nitro-glycerine.

~The Schultze-Tieman Method~ for determining nitrogen in nitro-explosives, especially nitro-cellulose and nitro-glycerine.--The figure (No. 44) shows the general arrangement of the apparatus. I am indebted for the following description of the method of working it to my friend, Mr William Bate, of Hayle. To fill the apparatus with the soda solution, the gas burette is put on the indiarubber stopper of basin W, and firmly clamped down. Then the taps A and C are opened, and B closed. When the burette is filled with soda solution half-way up the funnel Y, A and C are closed, and B opened. The arrows show the inlet and outlet for the cooling water that is kept running through the water jacket round the nitrometer tube. To collect the gas, raise the nitrometer off the rubber stopper, and place the gas tube from the decomposition apparatus in the glass dish W and under the opening of the nitrometer.

For the estimation of nitrogen in nitro-cellulose take .5 to .65 grm., and place in the decomposition flask _f_ (Fig. 45), washing in with about 25 c.c. of water by alternately opening clips D and E. The air in the flask is driven out by boiling, whilst the air is shut off by the tube _i_ dipping into the basin W, which is filled with the soda lye, and tube K is placed in the test tube R, which contains a few c.c. of water. As soon as all the air is completely driven out, clips D and E are closed, and the gas jet is taken away. (This flask must be a strong one, or it will burst.) Into test tube R, 25 c.c. of concentrated solution of protochloride of iron and 10 to 15 c.c. concentrated hydrochloric acid are poured, which are sucked up into the developing flask _f_ by opening clip E, air being carefully kept from entering. The clip E is now closed, and tube _i_ is put underneath the burette, and the development of NO gas is commenced by heating the contents of the flask _f_. When the pressure of the gas in the flask has become greater than the pressure of the atmosphere, the connecting tube begins to swell at _i_, whereupon clip D is opened, and the boiling continued with frequent shaking of the bulb, until no more nitrous gas bubbles rise up into the soda lye, the distilling over of the HCl causes a crackling noise, the clip D is closed, and E opened. The burette is again put hermetically on the indiarubber stopper in basin W, and the apparatus is left to cool until the water discharged through P shows the same temperature as the water flowing through (into the cooling jacket) Z. If the level of the soda solution in the tube X is now put on exactly the same level as that in the burette by lowering or elevating the tube X as required, the volume of NO obtained in c.c. can be read off within 1/10 c.c., and the percentage of nitrogen calculated by the usual formula.

The solution of protochloride of iron is obtained by dissolving iron nails, &c., in concentrated HCl, the iron being in excess. When the development of hydrogen ceases, it is necessary to filter warm through a paper filter, and acidify filtrate with a few drops of HCl. The soda solution used has a sp. gr. of 1.210 to 1.260; equals 25 deg. to 30 deg. B. The nitro-cellulose is dried in quantities of 2 grms. at 70 deg. C. during eight to ten hours, and then three hours in an exiccator over H_{2}SO_{4}. The results obtained with this apparatus are very accurate. The reaction is founded upon that of MM. Champion and Pellet's method.

~The Kjeldahl Method of Determining Nitrogen.~--This method, which has been so largely used by analysts for the determination of nitrogen in organic bodies, more especially perhaps in manures, was proposed by J. Kjeldahl,[A] of the Carlsberg Laboratory of Copenhagen. It was afterwards modified by Jodlbauer, of Munich,[B] and applied to the analysis of nitro- explosives by M. Chenel, of the Laboratoire Centrale des Poudres, whose method of procedure is as follows:--0.5 grm. of the finely powdered substance is digested in the cold with a solution of 1.2 grm. of phenol and 0.4 grm. phosphoric anhydride in 30 c.c. of sulphuric acid. The mixture is kept well shaken until the solution is complete. From 3 to 4 grms. of zinc-dust is then cautiously and gradually added, the temperature of the mass being kept down until complete reduction has been effected. Finally, 0.7 grm. of mercury is added, and the process continued in the usual way, according to Kjeldahl; that is, the liquid is distilled until all the ammonia has passed over, and is absorbed in the standard acid. The distillate is then titrated with standard ammonia.

[Footnote A: J. Kjeldahl, _Zeitschrift Anal. Chem._, 1883, xxii., p. 366.]

[Footnote B: Jodlbauer, _Chemisches Centralblatt_, 1886, pp. 434-484. See also _Arms and Explosives_, 1893, p. 87.]

The NO_{2} group is at the moment of solution fixed upon the phenol with the production of mono-nitro-phenol, which is afterwards reduced by the action of the zinc-dust into the amido derivative. During the subsequent combustion, the nitrogen of the amido-phenol becomes fixed in the state of ammonia. M. Chenel is perfectly satisfied with the results obtained, but he points out that the success of the operation depends upon the complete conversion of the phenol into the mono-nitro derivatives. This takes place whenever the organic compound forms a _clear solution_ in the cold sulphuric acid mixture. Substances like collodion or gun-cotton must be very finely divided for successful treatment. The following table shows some of the results obtained by M. Chenel:--

______________________________________________ | | | | | Total Nitrogen. | | Substances Analysed. |______________________| | | | | | | Calculated. | Found. | | |_____________|________| | | | | | Saltpetre (KNO_{3}) | 13.86 | 13.91 | | | | 13.82 | | | | 13.73 | | | | 13.96 | | Ammonium nitrate | 35.00 | 35.31 | | | | 34.90 | | | | 34.96 | | Barium nitrate | 10.72 | 10.67 | | | | 10.62 | | Nitro-glycerol | 18.50 | 18.45 | | Di-nitro-benzol[A] | 16.67 | 16.78 | | | | 16.57 | | Para-nitro-phenol | 10.07 | 10.03 | | Picric acid[A] | 18.34 | 18.42 | | | | 18.43 | | Ammonium picrate | 22.76 | 22.63 | | | | 22.67 | | Di-nitro-ortho-cresol | 14.14 | 14.10 | | | | 13.98 | | Tri-nitro-meta-cresol | 17.28 | 17.57 | | | | 17.27 | |_______________________|_____________|________|

[Footnote A: Dr. Bernard Dyer obtained 18.39 per cent. for picric acid and 16.54 per cent. for di-nitro-benzol.--_Jour. Chem. Soc._, Aug. 1895.]

When Chenel endeavoured to apply Jodlbauer's modification of Kjeldahl's process to the examination of the tri- and tetra-nitrated naphthalenes, he found that good results were not obtainable, because these compounds do not dissolve completely in the cold sulphuric acid. It may, however, be used if they are previously converted into the naphthylamines, according to the plan proposed by D'Aguiar and Lautemann (_Bull. Soc. Chim._, vol. iii., new series, p. 256). This is rapidly effected as follows:--Twelve grms. of iodine are gradually added to a solution of 2 grms. of phosphorus in about 15 or 20 c.c. of bisulphide of carbon, this solution being contained in a flask of 250 c.c. capacity. The flask and its contents are heated on the water bath at 100 deg. C. with constant attention, until the last traces of the carbon bisulphide have distilled away. It is then cooled, and the iodide of phosphorus is detached from the sides of the flask by shaking, but not expelled. The next step is to add about 0.5 to 0.6 grm. of the substance that is to be analysed, after which 8 grms. of water are introduced, and the flask is agitated gently two or three times. As soon as the reaction becomes lively, the contents of the flask are well shaken. It is usually finished about one minute after the addition of the water. The flask is now cooled, and 25 c.c. of sulphuric acid, together with 0.7 grm. of mercury, are gradually added; hydriodic acid (HI) forms, and the temperature of the flask must be raised sufficiently to expel it. The remaining part of the operation is as in the ordinary Kjeldahl process.

M. Chenel has found this process the best for the analysis of the nitro- naphthalenes, and for impervious substances like collodion or gun-cotton. Personally, I have never been able to obtain satisfactory results with this process in the analysis of nitro-cellulose, and I am of opinion that the process does not possess any advantage over the nitrometer method, at any rate for the analysis of gun-cotton.

Table giving the Percentages of Nitrogen and Oxide of Nitrogen in Various Substances used in or as Explosives:

Name FORMULAE NITROGEN NO_{2}
per cent. per cent.

Nitroglycerine C_{3}H_{5}(ONO_{2})_{3} 18.50 = 60.70 Hexa-nitro-cellulose C_{12}H_{14}O_{4}(ONO_{2})_{6} 14.14 = 46.42 Penta-nitro-cellulose C_{6}H_{8}O_{5}(ONO_{2})_{5} 11.11 = 36.50 Nitro-benzene C_{6}H_{5}NO_{2} 11.38 = 37.39 Di-nitro-benzene C_{6}H_{4}(NO_{2})_{2} 16.67 = 54.77 Tri-nitro-benzene C_{6}H_{3}(NO_{2})_{3} 19.24 = 63.22 Nitro-toluene C_{7}H_{7}NO_{2} 10.21 = 33.49 Nitro-naphthalene C_{10}H_{7}NO_{2} 8.09 = 26.53 Di-nitro-naphthalene C_{10}H_{6}(NO_{2})_{2} 12.84 = 42.12 Nitro-mannite C_{6}H_{7}(NO_{3})_{6} 23.59 = 77.37 Nitro-starch C_{6}H_{8}O_{4}(HNO_{3}) 6.76 = 22.18 Picric acid (Tri-nitro-phenol) C_{6}H_{2}OH(NO_{2})_{3} 18.34 = 60.15 Chloro-nitro-benzene C_{6}H_{3}Cl(NO_{2})_{2} 13.82 = 45.43 Ammonium nitrate NH_{4}NO_{3} 35.00 = Sodium nitrate NaNO_{3} 16.47 = Potassium nitrate KNO_{3} 13.86 = Nitric acid HNO_{3} 22.22 = Barium nitrate Ba(NO_{3})_{2} 10.72 =

~Analysis of Celluloid.~--The finely divided celluloid is well stirred, by means of a platinum wire, with concentrated sulphuric acid in the cup of a Lunge nitrometer, and when dissolved the nitrogen determined in the solution in the usual way. To prevent interference from camphor, the following treatment is suggested by H. Zaunschirm (_Chem. Zeit._, xiv., 905). Dissolve a weighed quantity of the celluloid in a mixture of ether- alcohol, mixed with a weighed quantity of washed and ignited asbestos, or pumice-stone, dry, and disintegrate the mass, and afterwards extract the camphor with chloroform, dry, and weigh: then extract with absolute methyl-alcohol, evaporate, weigh, and examine the nitro-cellulose in the nitrometer.

~Picric Acid and Picrates.~--Picric acid is soluble in hot water, and to the extent of 1 part in 100 in cold water, also in ether, chloroform, glycerine, 10 per cent. soda solution, alcohol, amylic alcohol, carbon bisulphide, benzene, and petroleum. If a solution of picric acid be boiled with a strong solution of potassium cyanide, a deep red liquid is produced, owing to the formation of potassium iso-purpurate, which crystallises in small reddish-brown plates with a beetle-green lustre. This, by reaction with ammonium chloride, gives ammonium iso-purpurate (NH_{4}C_{8}H_{4}N_{5}O_{6}), or artificial murexide, which dies silk and wool a beautiful red colour. On adding barium chloride to either of the above salts, a vermilion-red precipitate was formed, consisting of barium iso-purpurate. With ammonio-sulphate of copper, solutions of picric acid give a bright green precipitate. Mr A.H. Allen gives the following methods for the assay of commercial picric acid, in his "Commercial Organic Analysis":--

~Resinous and Tarry matters~ are not unfrequently present. They are left insoluble on dissolving the sample in boiling water. The separation is more perfect if the hot solution be exactly neutralised by caustic soda.

~Sulphuric Acid, Hydrochloric Acid, and Oxalic Acid~, and their salts are detected by adding to the filtered aqueous solution of the sample solutions of the picrates of barium, silver, and calcium. These salts are readily made by boiling picric acid with the carbonates of the respective metals and filtering: other soluble salts of these methods may be substituted for the picrates, but they are less satisfactory.

~Nitric Acid~ may be detected by the red fumes evolved on warming the sample with copper turnings.

~Inorganic Impurities and Picrates of Potash and Sodium~, &c., leave residues on cautious ignition.

~General Impurities and Adulterations~ may be detected and determined by shaking 1 grm. of the sample of acid in a graduated tube with 25 c.c. of ether, the pure acid dissolves, while any oxalic acid, nitrates, picrates, boric acid, alum, sugar, &c., will be left insoluble, and after removal of the ethereal liquid, may be readily identified and determined. For the detection and determination of water and of oxalic acid, 50 c.c. of warm benzene may be advantageously substituted for ether. Sugar may be separated from the other impurities by treating the residue insoluble in ether or benzene with rectified spirit, in which sugar and boric acid alone will dissolve. If boric acid be present, the alcoholic solution will burn with a green flame. Mono- and di-nitrophenic acids lower the melting point (122 deg. C). Their calcium salts are less soluble than the picrate, and may be approximately separated from it by fractional crystallisation, or by precipitating the hot saturated solution of the sample with excess of lime water. Picric acid may be determined by extracting the acidulated aqueous solution by agitation with ether or benzene, and subsequently removing and evaporating off the solvent. It may also be precipitated as the potassium salt.

~Potassium Picrate~ [KC_{6}H_{2}(NO_{2})_{3}O]. When a strong solution of picric acid is neutralised by carbonate of potash, this salt is thrown down in yellow crystalline needles, which require 260 parts of cold or 14 parts of hot water for their solution. In alcohol it is much less soluble.

~Ammonium Picrate~ is more soluble in water than the above, and sodium picrate is readily soluble in water, but nearly insoluble in solution of sodium carbonate.

~Picrates of the Alkaloids.~--Picric acid forms insoluble salts with many of the alkaloids, and picric acid may be determined in the following manner:--To the solution of picric acid, or a picrate, add a solution of sulphate of cinchonine acidulated with H_{2}SO_{4}. The precipitated picrate of cinchonine [C_{20}H_{24}N_{2}O(C_{6}H_{2}N_{3}O_{7})_{2}] is washed with cold water, rinsed off the filter into a porcelain crucible or dish, the water evaporated on the water bath, and the residual salt weighed. Its weight, multiplied by .6123, gives the quantity of picric acid in the sample taken.

~Analysis of Glycerine.~[A] Glycerine that is to be used for the manufacture of nitro-glycerine should have a minimum specific gravity of 1.261 at 15 deg. C. This can be determined, either by the aid of a Sartorius specific gravity balance, or by using an ordinary specific gravity bottle. One of 10 or 25 c.c. capacity is very convenient.

[Footnote A: See also Sulman and Berry, _Analyst_, xi., 12-34, and Allen's "Commercial Organic Analysis," vol. ii., part i.]

~Residue~[A] left upon evaporation should not be more than 0.25 per cent. To determine this, take 25 grms. of the glycerine, and evaporate it at a temperature of about 160 deg. C. in a platinum basin, and finish in an air bath. Weigh until constant weight is obtained. Afterwards incinerate over a bunsen burner, and weigh the ash.

[Footnote A: Organic matter up to .6 per cent. is not always prejudicial to the nitrating quantities of a glycerine.]

~Silver Test.~ A portion of the sample of glycerine to be tested should be put in a small weighing bottle, and a quarter of its bulk of N/10 silver nitrate solution added to it, then shake it, and place in a dark cupboard for fifteen minutes. It must be pronounced bad if it becomes black or dark brown within that time (acrolein, formic, and butyric acids).

The German official test for glycerine for pharmaceutical purposes is much more stringent, 1 c.c. of glycerine heated to boiling with 1 c.c. of ammonia solution and three drops of silver nitrate solution must give neither colour or precipitate within five minutes.

~Nitration.~ Fifty grms. of the glycerine are poured from a beaker into a mixture of concentrated nitric acid (specific gravity 1.53) and sulphuric acid (1.84), mixed in the proportions of 3 HNO_{3} to 5 H_{2}SO_{4} (about 400 c.c. of mixed acids). The mixed acids should be put into a rather large beaker, and held in the right hand in a basin of water, and the glycerine slowly poured into them from a smaller one held in the left. A constant rotatory motion should be given to the beaker in which the nitration is performed. When all the glycerine has been added, and the mixture has been shaken for a few minutes longer, it is poured into a separator, and allowed to stand for some time. It should, if the glycerine is a good one, have separated from the mixed acids in ten minutes, and the line of demarcation between the nitro-glycerine and the acid should be clear and sharp, neither should there be any white flocculent matter suspended in the liquid. The excess of acids is now drawn off, and the nitro-glycerine shaken once or twice with a warm solution of carbonate of soda, and afterwards with water alone. The nitro-glycerine is then drawn off into a weighed beaker, the surface dried with a piece of filter paper, and weighed; 100 parts of a good glycerine should yield about 230 of nitro-glycerine. A quicker method is to take only 10 c.c. of the glycerine, of which the specific gravity is already known, nitrate as before, and pour into a burette, read off the volume of nitro-glycerine in c.c. and multiply them by 1.6 (the specific gravity of nitro-glycerine), thus: 10 grms. gave 14.5 c.c. nitro-glycerine, and 14.5 x 1.6 = 23.2 grms., therefore 100 would give 232 grms. nitro-glycerine. The points to be noted in the nitration of a sample of glycerine are: the separation should be sharp, and within half an hour or less, and there should be no white flocculent matter formed, especially when the carbonate of soda solution is added.

~Total Acid Equivalent.~ Mr G.E. Barton (_Jour. Amer. Chem. Soc._, 1895) proposes to determine thus: 100 c.c. of glycerine are diluted to 300 c.c. in a beaker, a few drops of a 1 per cent. solution of phenolphthalein and 10 c.c. of normal caustic soda solution are added; after boiling, the liquid is titrated with normal hydrochloric acid (fatty acids are thus indicated and roughly determined).

~Neutrality.~ The same chemist determines the neutrality of glycerine thus: 50 c.c. of glycerine mixed with 100 c.c. of water and a few drops of alcoholic phenolphthalein[A] are titrated with hydrochloric acid or sodium hydroxide; not more than 0.3 c.c. normal hydrochloric acid or normal soda solution should be required to render the sample neutral; raw glycerines contain from .5 to 1.0 per cent. of sodium carbonate.

[Footnote A: Sulman and Berry prefer litmus as indicator.]

~Determination of Free Fatty Acids.~ A weighed quantity of the glycerine is shaken up with some neutral ether in a separating funnel, the glycerine allowed to settle, drawn off, and the ether washed with three separate lots of water. The water must have been recently boiled, and be quite free from CO_{2}. All the free fatty acid is now in the ether, and no other soluble acid. A drop of phenolphthalein is now added, a little water, and the acidity determined by titration with deci-normal baryta solution, and the baryta solution taken calculated as oleic acid.

~Combined Fatty Acid.~ About 30 grms. of the glycerine are placed in a flask, and to it is added about half a grm. of caustic soda in solution. The mixture is heated for ten minutes at 150 deg. C. After cooling some pure ether is added to it, and enough dilute H_{2}SO_{4} to render it distinctly acid. It is well shaken. All the fatty acids go into the ether. The aqueous solution is then removed, and the ether well washed to remove all H_{2}SO_{4}. After the addition of phenolphthalein the acid is titrated, and the amount used calculated into oleic acid. From this total amount of fatty acids the free fatty acid is deducted, and the quantity of combined fatty acids thus obtained.

~Impurities.~ The following impurities may be found in bad samples of glycerine:--Lead, arsenic, lime, chlorine, sulphuric acid, thio-sulphates, sulphides, cyanogen compounds, organic acids (especially oleic acid and fatty acids[A]), rosin products, and other organic bodies. It is also said to be adulterated with sugar and glucose dextrine. Traces of sulphuric acid and arsenic may be allowed, also very small traces indeed of lime and chlorine.

[Footnote A: These substances often cause trouble in nitrating, white flocculent matter being formed during the process of washing.]

The organic acids, formic and butyric acids may be detected by heating a sample of the glycerine in a test tube with alcohol and sulphuric acid, when, if present, compound ethers, such as ethylic formate and butyrate, the former smelling like peaches and the latter of pine-apple, will be formed.

~Oleic Acid~, if present in large quantity, will come down upon diluting the sample with water, but smaller quantities may be detected by passing a current of nitrogen peroxide, N_{2}O_{4} (obtained by heating lead nitrate), through the diluted sample, when a white flocculent precipitate of elaidic acid, which is less soluble than oleic acid, will be thrown down. By agitating glycerol with chloroform, fatty acids, rosin oil, and some other impurities are dissolved, while certain others form a turbid layer between the chloroform and the supernatant liquid. On separating the chloroform and evaporating it to dryness, a residue is obtained which may be further examined.

~Sodium Chloride~ can be determined in 100 c.c. of the glycerine by adding a little water, neutralised with sodium carbonate, and then titrated with a deci-normal solution of silver nitrate, using potassium chromate as indicator.

~Organic Impurities~ of various kinds occur in crude glycerine, and are mostly objectionable. Their sum may be determined with fair accuracy by Sulman and Berry's method: 50 grms. of the sample are diluted with twice its measure of water, carefully neutralised with acetic acid, and warmed to expel carbonic acid; when cold, a solution of basic lead acetate is added in slight but distinct excess, and the mixture well agitated. The formation of an abundant precipitate, which rapidly subsides, is an indication of considerable impurity in the sample. To ascertain its amount, the precipitate is first washed by decantation, and then collected on a tared, or preferably a double counter-poised filter, where it is further washed, dried at 100 deg. to 105 deg. C., and weighed. The precipitate and filter paper are then ignited separately in porcelain, at a low red heat, the residues moistened with a few drops of nitric acid and reignited; the weight of the lead oxide deducted from that of the original precipitate gives the weight of the organic matter precipitated by the lead. Raw glycerines contain from 0.5 to 1.0 per cent.

~Albuminous Matters.~ An approximate determination of the albuminous matters may be made by precipitating with basic lead acetate as already described, and determining the nitrogen by the Kjeldahl method; the nitrogen multiplied by 6.25 gives the amount of albuminous matter in the precipitate.

~The Determination of Glycerine.~ The acetin method of Benedikt and Canton depends upon the conversion of glycerine into triacetin, and the saponification of the latter, and reduces the estimation of glycerine to an acidmetric method. About 1.5 grm. of crude glycerine is heated to boiling with 7 grms. of acetic anhydride, and 3 to 4 grms. of anhydrous sodium acetate, under an upright condenser for one and a half hours. After cooling, 50 c.c. of water are added, and the mixture heated until all the triacetin has dissolved. The liquid is then filtered into a large flask, the residue on the filter is well washed with water, the filtrate quite cooled, phenolphthalein is added and the fluid exactly neutralised with a dilute (2 to 3 per cent.) solution of alkali. Twenty-five c.c. of a 10 per cent. caustic soda solution, which must be accurately standardised upon normal acid, are then pipetted into the liquid, which is heated to boiling for ten minutes to saponify the triacetin, and the excess of alkali is then titrated back with normal acid. One c.c. of normal acid corresponds to .03067 grm. of glycerine.

~Precautions.~--The heating must be done with a reflux condenser, the triacetin being somewhat volatile. The sodium acetate used must be quite anhydrous, or the conversion of the glycerine to triacetyl is imperfect. Triacetin in contact with water gradually decomposes. After acetylation is complete, therefore, the operations must be conducted as rapidly as possible. It is necessary to neutralise the free acetic acid very cautiously, and with rapid agitation, so that the alkali may not be locally in excess.

~The Lead Oxide Method.~--Two grms. of sample are mixed with about 40 grms. of pure litharge, and heated in an air bath to 130 deg. C. until the weight becomes constant, care being taken that the litharge is free from such lead compounds and other substances as might injuriously affect the results, and that the heating of the mixture takes place in an air bath free from carbonic acid. The increase in weight in the litharge, minus the weight of substance not volatilisable from 2 grms. of glycerine at 160 deg. C., multiplied by the factor 1.243, is taken as the weight of glycerine in the 2 grms. of sample. The glycerine must be fairly pure, and free from resinous substances and SO_{3}, to give good results by this process.

~Analysis of the "Waste Acids" from the Manufacture of Nitro-Glycerine or Gun-Cotton.~ Determine the specific gravity by the specific gravity bottle or hydrometer, and the oxides of nitrogen by the permanganate method described under nitro-glycerine. Now determine the total acidity of the mixture by means of a tenth normal solution of sodium hydrate, and calculate it as nitric acid (HNO_{3}), then determine the nitric acid by means of Lunge nitrometer, and subtract percentage found from total acidity, and calculate the difference into sulphuric acid, thus:--

Total acidity equals 97.46 per cent.--11.07 per cent. HNO_{3} = 86.39 per cent., then (86.39 x 49)/63 = 67.20 per cent. H_{2}SO_{4}.

Then analysis of sample will be:--

_ Sulphuric acid = 67.20 per cent. | Nitric acid = 11.07 " |- Specific gravity = 1.7075. Water = 12.73 " _|

This method is accurate enough for general use in the nitric acid factory. The acid mixture may be taken by volume for determining nitric oxide in nitrometer. Two c.c. is a convenient quantity in the above case, then 2 x 1.7075 (specific gravity) = 3.414 grms. taken, gave 145 c.c. NO (barometer = 748 mm, and temperature = 15 deg.C.) equals 134.9 c.c. (corr.) and as 1 c.c. NO = .0282 grm. HNO_{3} 135 x .0282 = .378 grm. = 11.07 per cent. nitric acid.

~Sodium Nitrate.~ Determine moisture and chlorine by the usual methods, and the total, NaNO_{3}, by means of nitrometer--0.45 grm. is a very convenient quantity to work on (gives about 123 c.c. gas); grind very fine, and dissolve in a very little hot water in the cup of the nitrometer; use about 15 c.c. concentrated H_{2}SO_{4}. One cubic cent. of NO equals .003805 grm. of NaNO_{3}. The insoluble matter, both organic and inorganic, should also be determined, also sulphate of soda and lime tested for.

~Analysis of Mercury Fulminate (Divers and Kawakita's Method).~--A weighed quantity of mercury fulminate is added to excess, but measured quantity of fuming hydrochloric acid contained in a retort connected with a receiver holding water. After heating for some time, the contents of the retort and receiver are mixed and diluted, and the mercury is precipitated by hydrogen sulphide. By warming and exposure to the air in open vessels the hydrogen sulphide is for the most part dissipated. The solution is then titrated with potassium hydroxide (KOH), as well as another quantity of hydrochloric acid, equal to that used with the fulminate. As the mercury chloride is reconverted into hydrochloric acid by the hydrogen sulphide, and as the hydroxylamine does not neutralise to litmus the hydrochloric acid combined with it, there is an equal amount of hydrochloric acid free or available in the two solutions. Any excess of acid in the one which has received the fulminate will therefore be due to the formic acid generated from the fulminate. Dr. Divers and M. Kawakita, working by this method, have obtained 31.31 per cent. formic acid, instead of 32.40 required by theory. (_Jour. Chem. Soc._, p. 17, 1884.)

Divers and Kawakita proceed thus: 2.351 grms. dissolved, as already described, in HCl, and afterwards diluted, gave mercury sulphide equal to 70.40 per cent. mercury. The same solution, after removal of mercury, titrated by iodine for hydroxylamine, gave nitrogen equal to 9.85 per cent., and when evaporated with hydroxyl ammonium chloride equal to 9.55 per cent. A solution of 2.6665 grms. fulminate in HCl of known amount, after removal of mercury by hydrogen sulphide, gave by titration with potassium hydrate, formic acid equal to 8.17 per cent. of carbon. Collecting and comparing with calculation from formula we get--

Calc. I. II. III.

Mercury 70.42 70.40 ... ... Nitrogen 9.86 9.85 9.55 ... Carbon 8.45 ... ... 8.17 Oxygen 11.27 ... ... ... _______

100.00

~The Analysis of Cap Composition.~--Messrs F.W. Jones and F.A. Willcox (_Chem. News_, Dec. 11, 1896) have proposed the following process for the analysis of this substance:--Cap composition usually consists of the ingredients--potassium chlorate, antimony sulphide, and mercury fulminate, and to estimate these substances in the presence of each other by ordinary analytical methods is a difficult process. Since the separation of antimony sulphide and mercury fulminate in the presence of potassium chlorate necessitates the treatment of the mixture with hydrochloric acid, and this produces an evolution of hydrogen sulphide from the sulphide, and a consequent precipitation of sulphur; and potassium chlorate cannot be separated from the other ingredients by treatment with water, owing to the appreciable solubility of mercury fulminate in cold water.

In the course of some experiments on the solubility of mercury fulminate Messrs Jones and Willcox observed that this body was readily soluble in acetone and other ethereal solvents when they were saturated with ammonia gas, and that chlorate of potash and sulphide of antimony were insoluble in pure acetone saturated with ammonia; these observations at once afforded a simple method of separating the three ingredients of cap composition. By employing this solution of acetone and ammonia an analysis can be made in a comparatively short time, and yields results of sufficient accuracy for all technical purposes. The following are the details of the process:--

A tared filter paper is placed in a funnel to the neck of which has been fitted a piece of rubber tubing provided with a clip. The paper is moistened with a solution of acetone and ammonia, the cap composition is weighed off directly on to the filter paper and is then covered with the solution of acetone and ammonia and allowed to stand thirty-four hours. It is then washed repeatedly with the same solution until the washings give no coloration with ammonium sulphide, and afterwards washed with acetone until washings give no residue on evaporation dried and weighed. The paper is again put in the funnel and washed with water until free from potassium chlorate, dried and weighed.

If _c_ = weight of composition taken,
_d_ = " " filter paper,
_a_ = " after first extraction,
_b_ = " " second extraction,
then _c+d-a_ = weight of fulminate,
_c+d-a-b_ = " " KClO_{3},
_b-d_ = " " sulphide of antimony.

The composition should be finely ground in an agate mortar.

The results of the analysis by this method of two mixtures of known composition are given below--

________________________________________________________________________ | | | | | | A | B | | | | | | | Percentage | Percentage | Percentage | Percentage | | | Taken. | Found. | Taken. | Found. | |____________________|____________|____________|____________|____________| | | | | | | | Antimony Sulphide | 36.47 | 36.25 | 37.34 | 37.22 | | Potassium Chlorate | 33.25 | 33.71 | 46.03 | 46.43 | | Mercury Fulminate | 30.27 | 30.02 | 16.61 | 16.34 | |____________________|____________|____________|____________|____________|

Dr. H.W. Brownsdon's (_Jour. Soc. Chem. Ind._, xxiv., April 1905) process is as follows:--The cap composition is removed by squeezing the cap with pliers, while held over a porcelain basin of about 200 c.c. capacity, and removing the loosened foil and broken composition by means of a pointed wooden chip. Composition adhering to the shell or foil is loosened by alcohol, and washed into the dish by means of alcohol in a small wash bottle. The shell and foil are put to one side and subsequently weighed when dry. The composition in the dish is broken down quite fine with a flat-headed glass rod, and the alcohol evaporated on the water bath till the residue is moist, but not quite dry, 25 c.c. of water are then added, and the composition well stirred from the bottom. After the addition of 0.5 grm. of pure sodium, thiosulphate, the contents of the dish, is well stirred for two and a half minutes. One drop of methyl orange is then added, and the solution titrated with N/20 sulphuric acid, which has been standardised against weighings of 0.05-0.1 grm. fulminate to which 25 c.c. of water is added in a porcelain dish, then 0.5 grm. of thiosulphate, and after stirring for two and a half minutes, titrated with N/20 sulphuric acid. The small amount of antimony sulphide present does not interfere with the recognition of the end point. After titration, the solution is filtered through a small 5-1/2 cm. filter paper, which retains the antimony sulphide. The filter paper containing the Sb_{2}S_{3} is well washed and then transferred to a large 6 by 1 test tube. Five c.c. of strong hydrochloric acid are added, and the contents of the tube boiled gently for a few seconds until the sulphide is dissolved and all the H_{2}S driven off or decomposed: 2-3 c.c. of a saturated solution of tartaric acid are added, and the contents of the tube washed into a 250 c.c. Erlenmeyer flask. The solution is then nearly neutralised with sodium carbonate, excess of bi-carbonate added, and after the addition of some starch solution titrated with N/20 iodine solution. This method for small quantities of stibnite is both quick and accurate, the error being about +-0.0003 grm. Sb_{2}S_{3} at the outside.

The tendency of this method is to give slightly low figures for the fulminate, but since these are uniform within a negligible error, it does not affect the value of the results as a criterion of uniformity. The following test results were obtained by Dr Brownsdon:--

____________________________________________________________ | | | | | Fulminate Taken. | Fulminate Found. | Error. | | Grm. | Grm. | Grm. | | | | | | 0.0086 | 0.0083 | -0.0003 | | 0.0082 | 0.0081 | -0.0001 | | 0.0074 | 0.0071 | -0.0003 | | 0.0068 | 0.0066 | -0.0002 | |____________________|___________________|___________________| | | | | | Stibnite Taken. |Sb_{2}S_{3}, Found.| Error. | | Grm. | Grm. | Grm. | | | | | | 0.0085 | 0.0084 | -0.0001 | | 0.0098 | 0.0099 | +0.0001 | | 0.0160 | 0.0157 | -0.0003 | | 0.0099 | 0.0100 | +0.0001 | |____________________|___________________|___________________|

TABLE FOR CORRECTION OF VOLUMES OF GASES FOR TEMPERATURE, GIVING THE DIVISOR FOR THE FORMULA.

V_{1} = V x B/(760 x (1 + dt)) (d = 0.003665) 1 + dt from 0 deg. to 30 deg. C.

___________________________________________________________
| | | | |
t. | 760x(1+dt). | t. | 760x(1+dt). | t. | 760x(1+dt).
_____|_____________|_____|_____________|_____|_____________
| | | | |
deg.C. | | deg.C. | | deg.C. |
0.0 | 750.000 | 1.7 | 764.7352 | 3.4 | 769.4704
.1 | 760.2785 | .8 | 765.0137 | .5 | 769.7489
.2 | 760.5571 | .9 | 765.2923 | .6 | 770.0274
.3 | 760.8356 | 2.0 | 765.5708 | .7 | 770.3060
.4 | 761.1142 | .1 | 765.8493 | .8 | 770.5845
.5 | 761.3927 | .2 | 766.1279 | .9 | 770.8631
.6 | 761.6712 | .3 | 766.4064 | 4.0 | 771.1416
.7 | 761.9498 | .4 | 766.6850 | .1 | 771.4201
.8 | 762.2283 | .5 | 766.9635 | .2 | 771.6987
.9 | 762.5069 | .6 | 767.2420 | .3 | 771.9772
1.0 | 762.7854 | .7 | 767.5206 | .4 | 772.2558
.1 | 763.0639 | .8 | 767.7991 | .5 | 772.5343
.2 | 763.3425 | .9 | 768.0777 | .6 | 772.8128
.3 | 763.6210 | 3.0 | 768.3562 | .7 | 773.0914
.4 | 763.8996 | .1 | 768.6347 | .8 | 773.3699
.5 | 764.1781 | .2 | 768.9133 | .9 | 773.6485
.6 | 764.4566 | .3 | 769.1918 | 5.0 | 773.9270
_____|_____________|_____|_____________|_____|_____________
___________________________________________________________
| | | | |
t. | 760x(1+dt). | t. | 760x(1+dt). | t. | 760x(1+dt).
_____|_____________|_____|_____________|_____|_____________
| | | | |
deg.C. | | deg.C. | | deg.C. |
5.1 | 774.2055 | .9 | 787.5755 | .7 | 800.9454
.2 | 774.4841 |10.0 | 787.8540 | .8 | 801.2239
.3 | 774.7626 | .1 | 788.1325 | .9 | 801.5025
.4 | 775.0412 | .2 | 788.4111 |15.0 | 801.7810
.5 | 775.3197 | .3 | 788.6896 | .1 | 802.0595
.6 | 775.5982 | .4 | 788.9682 | .2 | 802.3381
.7 | 775.8768 | .5 | 789.2467 | .3 | 802.6166
.8 | 776.1553 | .6 | 789.5252 | .4 | 802.8952
.9 | 776.4339 | .7 | 789.8038 | .5 | 803.1737
6.0 | 776.7124 | .8 | 790.0823 | .6 | 803.4522
.1 | 776.9909 | .9 | 790.3609 | .7 | 803.7308
.2 | 777.2695 |11.0 | 790.6394 | .8 | 804.0093
.3 | 777.5480 | .1 | 790.9179 | .9 | 804.2879
.4 | 777.8266 | .2 | 791.1965 |16.0 | 804.5664
.5 | 778.1051 | .3 | 791.4750 | .1 | 804.8449
.6 | 778.3836 | .4 | 791.7536 | .2 | 805.1235
.7 | 778.6622 | .5 | 792.0321 | .3 | 805.4020
.8 | 778.9407 | .6 | 792.3106 | .4 | 805.6806
.9 | 779.2193 | .7 | 792.5892 | .5 | 805.9591
7.0 | 779.4978 | .8 | 792.8677 | .6 | 806.2376
.1 | 779.7763 | .9 | 793.1463 | .7 | 806.5162
.2 | 780.0549 |12.0 | 793.4248 | .8 | 806.7947
.3 | 780.3334 | .1 | 793.7033 | .9 | 807.0733
.4 | 780.6120 | .2 | 793.9819 |17.0 | 807.3518
.5 | 780.8905 | .3 | 794.2604 | .1 | 807.6303
.6 | 781.1690 | .4 | 794.5390 | .2 | 807.9089
.7 | 781.4476 | .5 | 794.8175 | .3 | 808.1874
.8 | 781.7261 | .6 | 795.0960 | .4 | 808.4660
.9 | 782.0047 | .7 | 795.3746 | .5 | 808.7445
8.0 | 782.2832 | .8 | 795.6531 | .6 | 809.0230
.1 | 782.5617 | .9 | 795.9317 | .7 | 809.3016
.2 | 782.8403 |13.0 | 796.2102 | .8 | 809.5801
.3 | 783.1188 | .1 | 796.4887 | .9 | 809.8587
.4 | 783.3974 | .2 | 796.7673 |18.0 | 810.1372
.5 | 783.6959 | .3 | 797.0458 | .1 | 810.4175
.6 | 783.9544 | .4 | 797.3244 | .2 | 810.6943
.7 | 784.2330 | .5 | 797.6029 | .3 | 810.9728
.8 | 784.5115 | .6 | 797.8814 | .4 | 811.2514
.9 | 784.7901 | .7 | 798.1600 | .5 | 811.5299
9.0 | 785.0686 | .8 | 798.4385 | .6 | 811.8084
.1 | 785.3471 | .9 | 798.7171 | .7 | 812.0870
.2 | 785.6257 |14.0 | 798.9956 | .8 | 812.3655
.3 | 785.9042 | .1 | 799.2741 | .9 | 812.6441
.4 | 786.1828 | .2 | 799.5527 |19.0 | 812.9226
.5 | 786.4613 | .3 | 799.8312 | .1 | 813.2011
.6 | 786.7398 | .4 | 800.1098 | .2 | 813.4797
.7 | 787.0184 | .5 | 800.3883 | .3 | 813.7582
.8 | 787.2969 | .6 | 800.6668 | .4 | 814.0368
_____|_____________|_____|_____________|_____|_____________
___________________________________________________________
| | | | |
t. | 760x(1+dt). | t. | 760x(1+dt). | t. | 760x(1+dt).
_____|_____________|_____|_____________|_____|_____________
| | | | |
deg.C. | | deg.C. | | deg.C. |
19.5 | 814.3153 |23.0 | 824.0642 | .5 | 833.8131
.6 | 814.5938 | .1 | 824.3427 | .6 | 834.0916
.7 | 814.8724 | .2 | 824.6213 | .7 | 834.3702
.8 | 815.1500 | .3 | 824.8998 | .8 | 834.6487
.9 | 815.4925 | .4 | 825.1784 | .9 | 834.9273
20.0 | 815.7080 | .5 | 825.4569 |27.0 | 835.2058
.1 | 815.9865 | .6 | 825.7354 | .1 | 835.4843
.2 | 816.2651 | .7 | 826.0140 | .2 | 835.7629
.3 | 816.5436 | .8 | 826.2925 | .3 | 836.0414
.4 | 816.8222 | .9 | 826.5711 | .4 | 836.3200
.5 | 817.1007 |24.0 | 826.8496 | .5 | 836.5985
.6 | 817.3792 | .1 | 827.1281 | .6 | 836.8770
.7 | 817.6578 | .2 | 827.4067 | .7 | 837.1556
.8 | 817.9363 | .3 | 827.6852 | .8 | 837.4341
.9 | 818.2149 | .4 | 827.9638 | .9 | 837.7127
21.0 | 818.4934 | .5 | 828.2423 |28.0 | 837.9912
.1 | 818.7719 | .6 | 828.5208 | .1 | 838.2697
.2 | 819.0505 | .7 | 828.7994 | .2 | 838.5483
.3 | 819.3290 | .8 | 829.0779 | .3 | 838.8268
.4 | 819.6076 | .9 | 829.3565 | .4 | 839.1054
.5 | 819.8861 |25.0 | 829.6350 | .5 | 839.3839
.6 | 820.1646 | .1 | 829.9135 | .6 | 839.6624
.7 | 820.4432 | .2 | 830.1921 | .7 | 839.9410
.8 | 820.7217 | .3 | 830.4706 | .8 | 840.2195
.9 | 821.0003 | .4 | 830.7492 | .9 | 840.4981
22.0 | 821.2788 | .5 | 831.0277 |29.0 | 840.7766
.1 | 821.5573 | .6 | 831.3062 | .1 | 841.0551
.2 | 821.8859 | .7 | 831.5848 | .2 | 841.3337
.3 | 822.1144 | .8 | 831.8633 | .3 | 841.6122
.4 | 822.3930 | .9 | 832.1419 | .4 | 841.8908
.5 | 822.6715 |26.0 | 832.4204 | .5 | 842.1693
.6 | 822.9500 | .1 | 832.6989 | .6 | 842.4478
.7 | 823.2286 | .2 | 832.9775 | .7 | 842.7264
.8 | 823.5071 | .3 | 833.2560 | .8 | 843.0049
.9 | 823.7857 | .4 | 833.5346 | .9 | 843.2835
| | | |30.0 | 843.5620
_____|_____________|_____|_____________|_____|_____________