INDUSTRIAL A h T D ENGINEERING CHE*WISTRY
July, 1924
time a t a definite temperature and concentration of dissolving agent. What they actually obtained was the amount of material which dissolved in several hours’ time, while temperature and conrentration remained approximately constant, and while the surface of the material was changing slightly due to the quantity being dissolved. The amount of surface exposed per unit volume of material may be made very approximately the same by using material of the same mesh-in this case through 10 on 14. If, for comparison, a volume of material and therefore a surface corresponding to that a t the middle of the determination is used, the results will not be much in error because of change of surface during the experiment. Choosing as the unit of volume the volume occupied by 1 gram of quartz, then in terms of this surface the figures in Table I are obtained, showing loss in weight pw hour per equivalent surface.
703
DISCCSSION The effect of using a material in which the acid component is fully neutralized is marked. It may be noted in addition that the rate of solution of A when the boiler was operated at 43.6 kg. (120 pounds) pressure was greater than a t 109 kg. (250 pounds) pressure. This is in accord with the idea that the solubility of the silicates decreases with increase of temperature. Also, a re-run of A , even a t the lower pressure, gave a slower rate of solution than the primary experiment at the higher pressure. Probably incidental impurities were present in the initial run, which dissolved and affected the rate of solution. Another advantage of the minerals discussed over quartz is their greater specific gravity. This permits more rapid back-washing of the filter without loss of the filtering medium.
The Volumetric Determination of Fluorine’ By Wilfred W. Scott COLORADO SCHOOL OF MINRS,GOLDEN,Cor,o.
The Of LUORINE is comA brief reoiew is gioen of the more generally practiced methods though necessary in a gravimonly d e t e r m i n e d for the determination of fluorine. The method described by the metric method, is not necesgravimetrically by writer is the result of his experiences with the methods cited and is saryin a volumetric determibased on the principle of precipitation of fluorine as the calcium salt, nation of fluorine. Precipitation as lead chlorofluoride or as Calcium fluordepending upon its insolubility in acetic acid. Experiments were The Of phosphoric acid by silver nitrate, as recide. I n the second method conducted using fluorspar of tested purity, with prepared calcium ommended, with a subsethe Calcium is generally fluoride, and with alkali fluorides. Three procedures are dequent precipitation of the excess of silver as silver chlotreated with acetic acid to scribed: ( A ) determination of calcium and cquivalentfluorine, (B) remove ilnpurities, the Caldefermination of fluorine by the acetate method, and (C) r i d e ~requires e a e care, since silver phosphate cium fluoride being Practidetermination of fluorine in alkali fluorides. Experimental data may be quantitatively concally insoluble in this reare gioen showing the degree of accuracy that may be expected of verted i o silver chloride and agent. Two v o l u m e t r i c these procedures, sodium phosphate by addition of sodium chloride, as recmethod?, are generally ommended, thus defeating the k n o w n - - t h e method of purpose of the silver reagent. Ag,PO* 3KaC1 = 3AgCl f h’aaPO4 Greef, which depends upon the principle that a neutral aqueous solution of ferric chloride forms a white, crystalline precipitate with neutral solutions of alkali fluorides, making ~ ~ $ ~ ~ ~ ih $~ ~ ~ ~ ~~ e~ ~~ possible the titration of fluorine with ferric chloride; and the of silver for phosphate has to be relied upon for the removal of method 01’ Offerman. which evolves. bv sulfuric acid treatment. DhosDhoric acid. the fluorine as silicon tetrafluoride, with subsequent absorpIn the determination of fluorine by the first procedure tion of this fluoride in standard alkali, determination of the given, the writer obtained lower results than by the second excess of alkali giving the necessary data for obtaining the procedure. This low result was attributed to a partial defluorine absorbed. of calcium fluoride by sodium oxalate, as shown composition In a recent edition of Low’s work on ore analysis appears by the reaction a volumetric method for fluorine worked out by W. V. Norris, CaF2 NagC204 F? CaCsOc f 2NaF which depends upon the precipitation of fluorine from an The method outlined in this paper is a result of the writer’s acetic acid solution by addition of a measured amount of a standard solution of calcium acetate, the excess of which is a experience with the methods cited. Like the Korris method, measure of that required by fluorine: Norris removes the it is based on the principle of the second gravimetric method silica present in the solution by the method outlined in the given-the precipitation of fluorine as the calcium salt, deauthor’s work,2 and follows this by removal of phosphoric pending upon its insolubility in acetic acid. Details of the acid by means of silver nitrate. Two options are now given: procedure differ considerably from the other methods. Experiments were conducted with fluorspar of tested the first precipitates the excess of calcium, in presence of the calcium fluoride, by means of sodium oxalate, and titrates purity, with prepared calcium fluoride, and with alkali the calcium oxalate; the second method calls for a separa- fluorides. tion of solution containing the excess of calcium from the Experimental fluoride before attempting the calcium determination. FluorTwo procedures are suggested-a rapid method depending ine is calculated from the calcium removed from the solution, applying the formula CaFz to the compound formed. The upon the estimation of fluorine from the percentage of calcium writer’s experience with the Norris method led to the fol- present with fluorine, the calcium combined with commonly occurring substances being extracted by glacial acetic acid; lowing co~iclusions: and a procedure that depends upon separation of fluorine 1 Received December 13, 1923. from its combination by converting it to soluble alkali salt 2 “Standard &lethods of Chemical Analysis,” 3rd ed , p . 216.
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704
INDUSTRIAL AND ENGINEERING CHEMISTRY
and reprecipitating it from solution by addition of a known amount of calcium salt, the excess of the calcium being converted to oxalate and so determined, the amount combined with fluorine being thus estimated and the equivalent fluorine calculated. REAGENTS CALCIUM ACETATE (0.25 N solution)-l2.51 grams of pure calcium carbonate are dissolved in 500 cc. of water and 75 cc. glacial acetic acid (large beaker necessary) and the acetate formed is placed in a graduated flask and diluted to 1000 cc. The solution is standardized by precipitation of the calcium oxalate in an aliquot portion (40 cc.) and titration with standard potassium permanganate. Exact normality is recorded. 1 cc. 0.25 N solution = 0.005 gram calcium POTASSIUM PERMANGANATE (0.25 N solution)-7.91 grams of pure crystals (KMnOJ per liter are standardized against 0.67 gram of pure sodium oxalate equivalent to 40 cc. 0.25 N solution. Exact normality is recorded. SODIUM OXALATE (0.25 N solution containing 16.75 grams of the salt per liter)-Solution is best effected in hot water. (Solubility, 3.22 grams per 100 cc. at 15' C.)
PRELIMINARY PROCEDURE
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CONTAINING PHOSPHATES OR SULFATES-one ( a ) MINERALS gram of the finely powdered mineral, ore, or calcium fluoride salt is extracted with 50 cc. of dilute acetic acid (1 part glacial, 10 parts water) by gently warming for 15 to 20 minutes with stirring. The residue, transferred to a small, ashless filter, is washed with about 50 cc. of water making the total extract 100 cc. (Save for calcium determination, if desired.) The filter and residue are dried rapidly by spreading out on a watch glass. The fluoride is carefully transferred onto a sheet of glazed paper, the filter ignited, and the ash added to the fluoride. The residue is fused as directed under Fusion. Note.-For exact work an allowance has to be made for the solubility of the calcium fluoride. The following solubilities were found, 0.5-gram samples of material being taken and treated with 100 cc. of acetic acid of the strength stated: Acid Hz0 CaFz CaCOs CasPOc CaSOa 0.084 Very soluble 0.240 2 parts 0.0103 1 part 0.0144 Very soluble 0.276 0.170 1 part 10 parts
( b ) PHOSPHATES AND SULFATES ABSENT-NO acetic acid extraction is necessary. ( c ) SULFIDES PRESENT-SUlfUr as sulfide occurs generally combined with iron, copper, cobalt, etc. No special procedure is necessary here, as the sulfide is oxidized later.
FusIor\.-Five grams of sodium carbonate and 10 grams of potassium hydroxide, placed in a 50 to 60-tcc. silver or iron crucible, are brought to quiet fusion, and allowed to cool until a crust forms over the melt. Half a gram of the fluoride sample is intimately mixed with 0.5 to 1 gram of powdered silica prepared as outlined above (powdered sand free of fluorine will do), and placed in the crucible over the fusion. The crucible is covered and heat applied to bring the contents of the crucible to molten temperature. (High heat is not necessary.) Complete decomposition is effected in half to three-quarters of an hour. The crucible should be agitated frequently during fusion to mix the contents. Note.-Calcium fluoride is not so easily decomposed as many existing methods indicate. Hydrochloric acid apparently dissolves the mineral, but on dilution calcium fluoride precipitates. Sulfuric acid and potassium acid sulfate fusion is far from satisfactory; platinum is required and a loss due to bumping is liable t o occur. Complete decomposition b y acid treatment is frequently douhtful. The alkali fusion appears to be the best method for decomposing the fluoride.
If the mass is in molten condition,' it may be poured in the lid of the crucible; if too viscous to pour, it is spread over the inner surface of the crucible by rotating the crucible over the flame. The material is now disintegrated and removed from the crucible and lid by action of about 200 cc. of hot water in
Vol. 16, No. 7
a 500-cc. beaker. Ten cubic centimeters of hydrogen peroxide are added and the solution is boiled for about 5 minutes. Note -Fusions made in silver disintegrate more readily than those made in iron. Calcium carbonate tends t o adhere t o the walls of the crucible. Boiling the solution expels the excess of peroxide, which interferes in the oxaIate precipitation of calcium, if left in solution. Sulfides, iron, and other oxidizable materials are oxidized by the peroxide.
The solution containing the excess of sodium carbonate, potassium hydroxide, alkali fluoride, and the greater portion of the silica is filtered off; the residue, containing calcium carbonate (or phosphate if present in the fused material), silver, iron, some silica (10 to 15 per cent of total), etc., is washed with hot water (10 times) and the washings are combined with the first filtrate. The residue is used for Procedure A, the filtrate for Procedure B. Note -Should phosphates be present in the material, the greater portion will remain in the residue, and a small amount will pass into the filtrate as sodium salt. Cau(P0r)z 3NazC03 $ 3CaC03 2NaaP04
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PROCEDURE A-DETERMINATIONOF CALCIUM AND EQUIVALENT FLUORINE The residue washed into a beaker is dissolved in hydrochloric acid (200 cc. of water, 20 cc. HC1). If any gritty material remains it is advisable to fuse this with about 2 grams of sodium carbonate and 3 to 5 grams of potassium hydroxide, repeating the extraction with water ; the residue is dissolved in hydrochloric acid and added to A and the water extract to B. The free acid is neutralized with ammonia, the solution heated and filtered, and the residue washed. Calcium passes into solution, iron (and silver) remains on the filter. (The crucible should be rinsed out with dilute hydrochloric acid, as calcium carbonate may adhere to the walls of the vessel.) Note.-A small amount of calcium is liable to be occluded by the hydroxide of iron. I f this is present in appreciable amount i t is necessary to dissolve this in hydrochloric acid, reprecipitate with ammonia, and filter, adding the filtrate to the main portion containing calcium.
Calcium is now precipitated from the filtrate by adding 0.25 N sodium oxalate. About 60 cc. are necessary for 0.5 gram of calcium fluoride (fluorspar). After heating to crystallize the oxalate, the calcium is filtered off, washed with water (6 times), dissolved in water containing sulfuric acid (200 cc. H20 10 cc. HzS04),and titrated hot with 0.25 N potassium permanganate. 1 cc. 0.25 N KMnO4 = 0.005 gram Ca and 0 00474 gram F.
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Note.-If the mineral was extracted with dilute acetic acid (1 10) to remove calcium phosphate, carbonate, or sulfate, an allowance should be made for the solubility of calcium fluoride of approximately 0.014 gram CaFz per 100 cc. extract a t 1 8 O C. If total calcium is desited, the calcium in the extract should be determined and added to the calciam of the fluoride.
PROCEDURE B-DETERMINATIONOF FLUORINE. CALCIUM ACETATE METHOD The alkaline filtrate (water extract of the fusion) contains the fluorine, sodium and potassium salts, and silicic acid. The filtrate is heated to near boiling and sufficient 0.25 N calcium acetate reagent is added to precipitate all the fluorine and about 5 to 10 cc. excess (60 cc. per 0.5 gram CaF2). Glacial acetic acid is now added until faintly acid (if the solution is alkaline, litmus paper test) and then a n excess of 1 cc. per 100 cc. of solution. The heating is continued for about 5 minutes. Note.-Upon addition of the calcium acetate, calcium cat bonate also precipitates with calcium fluoride. When the solution becomes acid the carbonate dissolves. I f the acidity is correct, the precipitate settles readily and is easily filtered. Should i t he finely divided and remain in suspension, the addition of sufficient potaasium or sodium hydroxide to give an alkaline reaction will coagulate and settle the precipitate.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
July, 1924
The solution and precipitate are transferred to a 500-cc. (or larger) graduated volumetric flask and, after cooling (18” C.), made to volume, then transferred to a large beaker and the precipitate allowed to settle for a few minutes. An aliquot portion of the clear solution is decanted through a filter, the first 5 to 10 cc. being rejected (several filters may be used to hasten filtration, if slow). A measured volume of the filtrate is now taken for the determination of excess calcium. PRECIPITATION AKD TITRATION OF CALcIuni-Sufficient 0.25 N sodium oxalate solution is added to precipitate the calcium. It is safe to use as much oxalate as the aliquot requires in case no calcium was removed by fluorine-i. e., if one-half the total solution represents the aliquot, then 30 cc. of oxalate are added. The author prefers to precipitate the calcium from a weak acetic acid solution (about 0.5 cc. free glacial acetic acid per 100 cc.). This is the acidity of the solution obtained on adding calcium acetate and acetic acid, as directed, no alkali being added, as suggested for settling stubborn calcium fluoride precipitates. The calcium oxalate is coagulated by heating, then filtered, washed, and titrated with 0.25 iV potassium permanganate in a hot solution containing sulfuric acid. The oxalate is best dissolved from the filter by hot water containing sulfuric acid.
705
Experimental Data “(NHdzCOa added” indicates removal of silica by boiling with this reagyt. AgNOa added” indicates t h a t removal of phosphoric acid by silver has been attempted.
FLUORINE THEO-
OBTAINED RETICAL PROCEDURW Grams Grams Analysis of fluorsaar (NHdzCOa addid, AgN08 added. 20-minute 1 fusion. Procedure B 0.2313 0.2433 2 (NH4)zCOa added, AgNOs added. 30-minute fusion. Procedure B 0.2427 0.2433 3 (NHdzCOa added, AgNOs added. 30-minute fusion. Procedure B 0.4855 0.4807 4 (NHahCOs added, AnNOa added. 0.1439 0.4870 0.4807 gram phosphate added Procedure B. 0.1439 gram phosphateb and 0.4867 0.4807 0 . 5 gram FezOa added Procedure B. NaOH substituted for K O H in 0 0,4884 0.4807 fusion Procedure B. KnCOs in place of KOH, elec7 0.2410 0,2433 tric furnace Procedure B. 20-minute fusion with regular 8 0.2312 0.2433 mixture Procedure B 30-minute fusion with regular 9 mixture 0.4848 0.4807 Procedure B. 30-minute fusion with regular 10 0.4807 0.4807 mixture Procedure B. Titrating excess oxalate 11 0.2359 0.2433 reagent 12 Procedure B. Same sample titrating pptd. 0.2473 0.2433 calcium as in B Procedure B. Same sample titrating pptd. 13 0,2433 0.2417 calcium as in B 0,2428 0,2433 Procedure B. Fusion in silver crucible 14 0.2438 0.2433 15 Procedure B. Fusion in silver crucible Analysis of prepared CaFz Procedure B. Fusion in iron. Analysis of 16 CaFz salt 0.4826 0,4867 1 cc. 0.25 N potassium permanganate = 0.005 gram calcium. Procedure B. NazCOs and KzCOs fusion in 17 0.2433 oven a t 900” C. 0.2422 Procedure B. KzCOs and K O H fusion in silCAwuLArIow-If A = cc. 0.25 N calcium acetate 18 0.2433 ver crucible 0.2412 B = cc. 0.25 N potassium permanganate Analysis of alkali fEuorides X = factor for converting the aliquot por0.3270 0.3230 Potassium fluoride b y Procedure C tion of solution taken in the calcium 19 0,5002 0.4524 Sodium fluoride by Procedure C 20 determination to total solution Sodium fluoride by Procedure C, adding 1 21 0.4524 Then A cc. X B cc. = cc. 0 25 N calcium acetate required 0.4039 gram CaCOa and 1 gram SiOz and fusing Sodium fluoride.c Calcium determined in 22 by fluorine 0,3300 0.4524 presence of CaFz The difference multiplied by 0.005 = calcium combined with Fluorsoar decomoosed as usual and fluorine 23 fluorine, or multiplied by 0.006 = equivalent fluorine (Ca X calcdated fro& calcium by Procedure A (0,5108 Ca = 0 : 4845 F). Adding correc1.2 = I?). (See Discussion.) tion for solubihty of CaFz (extraction, 0,4867 0,4865 200 cc.) Correction -Owing to the slight solubility of calcium fluoride and pos0.4807 0.4844 Procedure A. Ca = 0.511 24 sibly to the foimation of a complex compound, calcium fluoride with n Procedure B, same sample, solution from A. fluosilicate, a corrective factor seems to be necessary, the ratio of calcium t o Combined Ca = 40.0. Using factor 1.2, 0.4872 eouivalent F = fluorine being 40 48, rather than the ratio represented in the foimuls Cap:. a No corrections applied for solubility of CaFz (0,002 gram CaFz per 100 cc., as this is included in factor 1.2). b Microcosmic salt. PROCEDURE C-DETERMINATIONIX ALKALIFLUORIDES c The sodium fluoride evidently contained silicon fluoride. Observe the lower results obtained in Expt. 21 to which ca!cium and Si02 are added and DECOMPOSITION-0.5to 1 gram of the alkali fluoride is where the material is fused. If the factor 1.2 IS applied, a s is the case in all B methods, the total fluoride in this sodium salt is about the same as obtained dissolved in about 100 cc. of hot water. in Expt. 20. Expt.
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PRECIPITATION-The fluorine is precipitated by adding, from a buret, a known amount of 0.25 N calcium acetate in sufficient amount to precipitate all the fluorine, and then 5 to 10 cc. in excess. If the solution has not become acid by addition of the reagent, make it so by adding acetic acid. The s o h tion and precipitate are transferred to a 250-cc. graduated flask, and after cooling are made to volume and well mixed. An aliquot portion is now filtered through a fine-mesh filter (rejecting the first 5 to 6 cc.). A measured portion (half the original total is recommended) is heated to boiling, and calcium is precipitated by adding an excess of sodium oxaIate. The solution is neutralized with ammonia and the calcium oxalate filtered off, washed, and titrated with 0.25 N potassium permanganate, according to the standard procedure. (See Precipitation and Titration of Calcium.) CALCULATIONS OF FLUORINE-
If A = total cc. of 0.25 N calcium acetate B = cc. of 0.25 N potassium permanganate required by the calcium in half the total volume Then A - 223 = per cent fluorine per half gram sample or A 2B X 0.005 X 0.948 = gram fluorine
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Note -It
appear4 t h a t the compound formed by addition of calcium acetate t o the soluble fluoride is CaFz; i t is thus possible to use the conversion factor 0 948 for converting the calcium, combined with fluoride, t o its equivalent fluoride The method does not distinguish fluorine combined as a fluosilicate from fluorine combined as a fluor*de
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Discussion MATERIALS USED Fluorspar was extracted with dilute acetic acid and the dried material used. The original mineral contained 51.08 per cent of calcium remaining from the acetic acid extraction, 0.47 per cent of acetic acid-soluble material (calcium present), and 48.45 per cent of fluorine remaining with acid-insoluble material. (b). Pure calcium fluoride, prepared by the action of hydrofluoric acid on calcium carbonate (in platinum), evaporation to dryness, extraction with dilute acetic acid, and ignition to dull red heat. The weight of calcium carbonate taken and the fluoride obtained corresponded closely with the ratio of CaCOs to CaFz. The fluorine determined in this material was a remarkable check on that in the fluorspar of (a). ( c ) Pure potassium fluoride. ( d ) Sodium fluoride. This material evidently contains a fluosilicate. (a) Pure calcium fluoride.
DECOMPOSITION OF MATERIAL The best method for decomposing fluorspar or calcium fluoride was found to be by fusion with sodium and potassium carbonates, sodium carbonate and potassium hydroxide, or sodium or potassium carbonate and sodium hydroxide. The presence of silica was necessary, Omitting silica resulted in B 52 per cent decomposition, the result for fluorine being a little over half of that present in the mineral. The addition of potassium hydroxide to sodium carbonate, as suggested in the
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INDUSTRIAL A X D ENGINEERING CHEiMZSTRY
Norris method, has the advantage of giving a flux with lower melting point, but being equally effective in decomposing the fluoride. This makes it possible to use silver crucibles for the fusions. There appears to be no advantage in using the sodium and potassium carbonate mixture a t higher heat. (See Expt. 17.) The use of silver in place of iron eliminates the necessity of a double precipitation of iron to obtain calcium; furthermore, the absence of iron appears to be an advantage in disintegrating the fusion with water. Iron crucibles are satisfactory, however, and are cheaper and more durable than silver. Nickel crucibles resist the fusion fairly well, but are not so satisfactory as silver or iron. S s calcium carbonate is apt to cling to the wall of the crucible, i t is frequently necessary to wash out the vessel with hydrochloric acid to obtain this in Procedure A.
PRESENCE OF SILIPAIN SOLCTION I n the gravimetric method for determining fluorine, the silica, which is always present in the solution from the fusion, has to be removed. The conventional method is to boil the solution with ammonium carbonate, thereby causing the precipitation of silica. This treatment requires considerable time and is unnecessary in the volumetric determination of fluorine. See Expts. 1, 2, and 3 and comparewith those by the regular procedure, omitting the removal of silica. SOLUBILITY O F CALCIUM CARBONATE The water extract of the fusion contained no appreciable amount of calcium; an attempt to precipitate calcium from this extract by addition of sodium oxalate gave negative results. The water-insoluble residue was found to contain 99.6 per cent of the calcium present in the original material. This represents a loss of 0.002 gram of calcium on the 0.5-gram sample taken. The addition of sodium or ammonium carbonate to the wash water will reduce the solubility of the carbonate. PHOSPHATES, SULFATES, AND CARBONATES These may be removed by extraction with dilute acetic acid as follows: The action of dilute acetic acid to remove calcium salts other than CaFz is shown by the experiment in which 1 gram CaFn, 5 grams CaC03, 0.25 gram of CaSOh, and 0 25 gram Cas(PO& were mixed and extracted with 200 cc. of 1: 10 acetic acid. The calcium, other than that combined with fluorine, weighs 0.3706 gram. The extracted calcium weighs 0.3975 gram. The difference, 0.0269 gram, was due to the solubility of CaFz in the acid.
Calcium. phosphate and calcium sulfate are practically insoluble in glacial acetic acid; hence the addition of water is necessary for this solvent. Calcium fluoride is slightly soluble in dilute acetic acid. Should any phosphate remain in the material, th.e greater portion of this will be found with the calcium carbonate residue, a small amount alone passing into the water extract, probably as sodium or potassium salt. The phosphate present in this solution does not interfere with the fluorine determination, although it is occluded by the calcium fluoride precipitate. Removal of phosphate by means of silver nitrate is unsatisfactory, as has been stated in the introductory portion of this paper.
PRECIPITATION OF CALCIUMOXALATEIS PRESEKCE OF CALCIUM FLUORIDE This procedure has already been pointed out a$ giving low results owing to the action of the oxalate reagent on the calcium fluoride. The writer found that sodium oxalate was more active in this regard than oxalic acid, as one would naturally suppose. The following comparison of results obtained on the same material confirmed this supposition:
Vol. 16, No. 7 Calcium Per cent
(a) (b) (c)
(d)
Regular procedure, sodium oxalate precipitation CaFz present Sodium oxalate precipitation in presence of CaFz Oxalic acid precipitation in presence of CaFz See Expt. 22
(no
40 * 26 26
31.10
PRECIPITATION OF CALcIuni FLUORIDE This is best effected by adding the calcium acetate reagent to the alkaline solution of the fluoride. The calcium carbonate, which also forms, redissolves as soon as the solution becomes acid. A large amount of acid is to be avoided, as this liberates silicic acid, which prevents the settling of the fluoride. When the solution is first acidified and the calcium fluoride is then precipitated, the compound settles badly and is difficult to filter. Should the fluoride be difficult to settle, it is preferable to make the solution alkaline by addition of sodium or potassium hydroxide, rather than to add an insoluble substance to carry down the flocculent material. The alkali treatment coagulates the fluoride (probably dissolving silicic acid) and causes rapid settling. I n the determination of calcium fluoride by Procedure B, consistently lower results are obtained than would be expected from the formula CaF2. The precipitate was examined and found to contain approximately 39 per cent calcium instead of over 51 per cent. This low percentage is due in part to the fact that a small portion of the silica in solution is precipitated with the fluoride so that the substance obtained is not a true compound. On the other hand, the consistently lower amount of calcium required by the fluorine present in the solution leads one to suspect that the compound formed under the conditions of the method is not calcium fluoride, but a complex compound of calcium fluoride with a silicofluoride. This assumption has not been confirmed. A second cause of low results may be the solubility of the calcium fluoride, the calcium in solution being precipitated as oxalate and calculated with that uncombined with fluorine. The presence of fluosilicic acid or of silicic acid may cause the difference between this procedure and that for soluble alkali fluorides. Then again, a third cause may be the occlusion of sodium or potassium fluoride by the calcium carbonate. In any case the calcium required by the fluorine in solution is apparently less than that required by the fluorine in the original material. It might be well to state here that the decomposition of the material is frequently the cause of low results, not only in Procedure I3 but also in A. This was shown by giving out samples of calcium fluoride to eighty-five students for titration of calcium. I n the first trial a few obtained theoretical results, a second trial with longer fusions made the majority obtain correct results. All titrations were conducted under the supervision of an instructor. It was noticed, especially in case of silver crucibles, that a coating of carbonate adhered to the crucible, which could not be removed by water or by a rubber-tipped glass rod. The product dissolved in dilute hydrochloric acid proved to be calcium carbonate. It is advisable, therefore, to wash out the crucible with dilute acid to obtain the total calcium of the material. The occlusion of calcium by ferric hydroxide is well known and has been mentioned under Procedure A. CONCLUSION The determination of fluorine in alkali fluorides may be accomplished with accuracy and rapidity by Procedure C. This, however, makes no distinction between fluorine combined as fluoride and that combined as a fluosilicate, total fluorine alone being determined. It is a peculiar fact that the addition of calcium carbonate with the usual fusion mixture of silica and afkalies, followed by fusion with the alkali
ILVDU S T R I A L A N D ESGINEERI,VG C H E X I S T R Y
July, 1924
fluoride, gives results corresponding with those obtained with calcium fluoride or fluorspar. This suggests that calcium may be responsible for the low fluorine results by Procedure B. The ratio of calcium to fluorine obtained by this procedure
707
would correspond to the ratio in a complex compound having the formula 8 CaFZ.CaSiF6, 1: 1.18. I n the absence of calcium, and omitting fusion, the compound formed by addition of the standard calcium salt appears to be CaF2.
Influence of Several Solvents on t h e H a n u s Iodine Values of Cottonseed and Coconut Oils' By Herman J. Bankston, Jr., and Frank C. Vilbrandt EMORY UNIVERSITY, ATLANTA, GA.,A N D UNIVERSITY OF NORTHCAROLINA, CHAPELHILL, N. C. EXPERIMEKTA L LTHOUGH the exThis article shows the influence of such solvents as chloroform, The procedure' was that tent to which an orcarbon tetrachloride, ether, ethyl alcohol, and benzene on the Hanus given as an official iodine ganic substance will iodine values of cottonseed oil with a high iodine value, and coconut method by the Association absorb bromine is claimed to oil, with a low iodine oalue. Chloroform and carbon tetrachloride of Official A g r i c u l t u r a l be indicative of the degree gioe higher and more consistent results than ether, alcohol, or benzene, Chemists,* except that the of unsaturation of the fats and their use is not attended with variations due to changes in the quantity of solvents was and oils of which it is comquantity of the solvents used. Chloroform seems to be the superior varied from 0 to 25 cc. I n posed, the iodine method solvent under the conditions studied. order t o eliminate as many is generally used in the factors as possible, 0.5-gram quantitative determination of this degree of unsaturation, the value thus obtained be- samples were used, first dissolved in the solvent, then treated ing used as one of the important tests in the evaluation of with 50 cc. of the Hanus iodine solution in the glass-stoppered bottles and allowed to react with frequent shaking a t 25" C. such organic bodies. It is wtdl known that the methods for the determination of for exactly 30 minutes. The excess iodine was then backthe unsaturation value of a n oil or fat by the iodine methods titrated with 0.1 N sodium thiosulfate solution. The iodine are empirical and lend themselves to considerable variance in solution was made approximately 0.1 ATstrength a t first, but the values obtained on the same sample, owing to differences it lost strength slowly and had t o be standardized each in time, concentration, nature of the oil, etc. Even with time it was used: The results are recorded in Table I. these factors carefully controlled, some laboratories suggest Iodine determinations were run on each of the solvents used the interchanging of the solvent used on the oil-i. e., the use and only those specimens were selected that showed no of chloroform, carbon tetrachloride, carbon disulfide, ether, or reaction with this reagent. 8 J . Assoc. O f i c i a l Agr. Chem , 2 , 305 (1916-17). benzene, as the carrier of the oil in order to assist in the speed of the reaction of the iodine on the oil. This practice is TABLE I-IODINE VALUGS OF COTTONSEED AND COCONUT OILSWITH VARIOUS SOLVENTS questionable, as the results of this investigation show. Maximum Chloroforp is uniformly used as the solvent of the oil in Volume of Variation in Solvent Individual the methods proposed by H a n q 2 Hubl,3 and Wallere4 I n Solvent c c. Runs addition, Hub1 used alcohol, not as the solvent for the oil, None None 1,38 but for the iodine; the influence of this alcohol was not 5 2.52 CCla 10 1.35 studied. The oil distributed itself between the chloro- CCla 15 0.30 form and the alcohol. I n the modifications of the iodine CCl4 25 0.47 5 0.10 methods as proposed by Ephraim,6 W i j ~ and , ~ Winkler,7 the CHCla CHCli 10 0.07 15 0.77 solvent for the oil was carbon tetrachloride. Wijs used car- CHCli CHCla 25 0.38 bon tetrachloride because he claimed the presence of some CzHiOH 5 2.20 CzH4OH 10 1.60 alcohol in chloroform made this reagent nndesirable. C~HIOH 15 3.30 CzHhOH 25 2 .30 Owing to the instability of carbon disulfide it cannot be CzHdz0 5 0.54 depended upon; hence it was deemed that it would find no CzHsIzO 10 0.11 2 0 15 1.70 general use as a solvent and was not studied in this investi- (CzHs (CzHJzO 25 1.50 CeHa 5 6.00 gation. CeHa 10 0.80 The Hanus method lends itself readily to the study of the CnHe 15 1.70 25 2.80 influence of various solvents, and was therefore used as the C6H6 8.5 None 10.0 9.6 basic method in this investigation. The oils used were cotton- None 10.9 9.8 10.2 9.8 2.40 seed oil with a fairly high iodine value, and coconut oil with a CClr 5 9.6 9.2 9.4 9.4 0.40 9 . 2 CClr 10 8 . 6 9 . 7 9 . 2 1.10 low value. Although benzene and ether are not proposed in CClr 11.6 15 11.1 10.5 11.1 1.10 10.7 25 the standard methods, they were included to determine their CClr 10.3 10.2 10.4 0.05 9.9 CHCli 5 9.0 8.9 2.10 7.8 limits of application. CHCls 10 9 4 9.7 9.7 10.0 0.60
A
1
Received January 26, 1924
Z . Nohv -Genussm , 1, 913 (19011, J Assoc O f i c r a l A g r Chem , 2,305 (1916-17) * Dinslers polytcch J , 263, 281 (1884). * Chem Z f g , 19, 1716, 1831 (1895) Z anqew Chem , 8 , 254 (1895). 8 B e y . , 31, 750 (1898). 7 C h t m Ztg , 39, 744 (1915).
CHCla CHCla CzHsOH CzHsOH CzHsOH CsHsOH (CzHs)zO (CzHs)zO (CzHs)zO C6Ha CnHs C6H6
15 25 5 10 15 25 5
10 25
5 10 15
9 7 11.6 2.2 1 23 2.45 2.54 7.3 10.7 4.1 6.0 7.67 5.3
9.2 10.9 3.4 2.9 3.27 3.82 6.9 9.08 3.8 7.0 6 93 4.5
9.9 1.0
7.1 9.9 3.5 2.0 8.50
9.5 10.8 2.2 2.1 2.86 3.18 7.1 9.89 3.8 5.0 7.67 4.9
0.59
1.70 2.40 1,67 0.82 1.28 0.4 1.62 0.6 5.0 1.57 0.8
