3 r; THE ANALYST. I___I___ -.__ -.--.-^---------_. NOTE UPON THE EBTIMATION OF PEROXIDE OF HYDROSEN WITH SPECIAL REE’ERENCE TO THE COb6MIERCUL PRACTICE OF SELLXNG). UPON VOLUME BTRENUTH, Rosoox and Schorlemmer. in &heir Treatise on Chemirstry (Vol. I, p. 261) give the fofiowing reaction as applicable for the voltun&riic estimation of Hydroxyl by means of potassio permanganate. 2K%ho4 + H202 + 8&804 = &SO4 + 2MnSQ + 4H,O + 30,. Hingzett, in a paper read before the Chemical Society (J. C. 8. xxxvii, 805), shtes it thus :- K2Mn208 + 5H,O2 + S&S04 = &SO, + 2MnS04 + 8H20 + 50,. As this assigprs to permanganate five times the value (in relation to hydroxyl) given to it by Roscoe and 8chorlemmer, we were induced to make some experimentar with the view of ascertaining which ie tihe oorreot one.The following reactions are theoretically possible :- (1.) &Mn,O, + Hg02 + 3-0, = &SO, + ~ M I S ~ , + 4 a-0 + 30, from lvhich 1 C.C. 4 yermanganate = *00034 gram K O 2 and evolvea a total of *00096 gram 0 = 067132 0.08, at 0’ and 760 m.m. pressure. from which 1 C.O. 3 permangamte = *00068 :gram K O , and evolves a total of ‘00113 gram = 078321 O.C. Oxygen. from which 1 C.C. $ pimanganate = *00102 gmm K O 2 tlnd evolve8 a tofd of *00128 gram = *ti961 C.C. Oxygen. fl*Olkk which 1 C.O. Pam = 1.007 cr.ee, oxygen. from which 1 C.C. $ permanganate =: *0017 gmm H202 and evo1ves.a total of *OOlG gram = 1*1188 c.ce. oxygen. (2.) &Mn208 3- 2H,0, + 3w0, = K@O, + 2MnS0, + 6&0 +3Q 02, (3.) $- 3H20, $- 3%SO4 = -0, $- 2MnSO, + 6H,O $- 40, (A) KJb,O, + iH,O, + 3H2S0, = K2&0, + SMnSO, + 7H20 + SiO,, permanganah = *00136 gram H,O, and ovdve8 total of *00144 (6.) &Mb,O, $- 6H2O2 + SHaO, =-&SO, $- 21KnS04 + 8&0 + 602, We decided first to titrate some samples with pemanganate; secondly to measure the gas liberated, and then in order to check these i*esults,’to employ’the process used by Kingzett, via :-Measuiing the iodine liberated by a known volume of solution of hydroxyl, with standwd sodic thiosdphate.PQI* the titration 10 ms. of hydroxyl were taken, mixed with 40 0.~13. of sulphuric a d (I : 3) and made up to 100 G.CS. with distilled water. The decinormal perman- ganate solutiou ~ 1 1 8 run in until a faint piuk tingo, peiulanenf for a few minutes became tlpp’&*THE ANALYST.37 _I__- ---_I__--__ -___--- The following iwulte were obtained :- rs'nt~lc A, sold ds 20 002s.-Slightly acid, contained Hz$04 and trace of HCI; 10 0.~8. left on evaporation 0012 gram residue, 10 o m . of the diluted solution requiscd 31.5 C,C. -$ K2Mn208. 10 - 9 9 9 ) Y , 31.7 9 , 10 9 , 9 , 9 9 31.6 9 , 10 9 ) 9 , 1 , 31.5 9 , 10 9 , ,) 9 , 31-7 9 , 10 9, 9 , 9 , 31-7 9 9 10 ,, 9 ) 9 ) 31.5 $ 9 10 9, $ 9 1, 31.6 Ayesage 31%3 C.U. " Accordixg to the five equations, the gas liberated. should nieasure respectively :- Equation1 ,, 31-63 x 97132 = 21.2338 c.cs'. ,, 2 .. 31.63 x m z i = 2-1-7729 ,, ,, 3 ,. 31.63 x 08951 = 28.312 9 , ,, 4 ,, 31*63 x 1.007 = 31.8514 ,, ,, 6 31.68 x 1.1185 = 35.3876 ,, Next 10 CAM. of the diluted acid solution were introduced into a small flask, the cork of which was furnished with two holes, through one of which a delivery tube connected with a iteceivor passed, and through the other the nozzle of a burette con- taining permanganato solution, fitted tightly.A quantity of permanganate, just sufficient to colour the contents of the flask permanently pink, was then run in, and the gas collected over mercury, the volume of solution used being deducted from that of the gas obtained, the residue reduced to standard temperature and pressure, and to this was added an amount equal to the capacity of the fluid in the flask for holding oxygen in solution at that temperature. The figures given below have been thus corrected :- .. * . .. .. .. .. .. .. 34.518 35.384 35.882 36.65 35.514 34.6 34.73 35-75 It is therefore apparent that the equations 1,2, and 3, do not represent the chauge ISanyZe &sold ccs 10 V O Z ~ ., was ueiitral; 10 c.cs. gave -0918 gram of residue containing which occws . ICC1 and ti*aces of Na,O and H,SO,. Diluted and acidified as before :-- 20 c m . of the dilute solution requised 9 , 2 ) .. 14.4 1 ) ), 9 , ,. 1 4 4 7 , 10 7 ) 10 7 , 10 9 ) 9 , ? 7 * . 14.5 1 , 10 ,? 9 , 9 , ,. 14.4 2 , 10 $ 9 9, 1 9 , . 14.4 9 , Avesage 14.43 c.cs. By cqutition 4 . , 14-63 x 1.007 = 14.331 c.cs. of gas ,, 6 .. 14-43 x 1.1188 = 16*144 ,, 10 C.W. of the dilute solution evolved . , 15.718 c.cs. of gas . , 14.5 c.cs. $ K,Mn,O, 10 ? ? 9 , 9 9 ., 15.921 ,? 10 1 , 7, 9 , .. 16.249 ,, 10 9 2 7 , 9 , ,, 15.793 ,, 10 9 , 1 9 73 .. 1G-173 ,, 10 ? ) >, $ 3 ,.13-iGS ),38 THE ANALYST. Banple C, sold rn 20 VO~S., was decidedly mid, contained SiO,, K20, H28U4, and traces of NhO and Hal; 10 c.cs. evaporated on a water bath, left *0374 gram of residue. Diluted and acidified as before :- 10 C.CLI. of the dilute solution required 9.7 C.C. % K,Mn,O, 10 C.CB. Y ? ) 9 9% 1 ) 10 c.m. ? 9 9, 0.S f ) 10 c.c.9. * ¶ >, 9*8 9 , 10 0.08. 9 , 8 ) 9.8 9 s 10 C.08. 1 , 3? 9-7 9 9 Average 9*73 c.os. By equation 4, , . 9-73 x I*007 = 9.708 c.us. of gas. ,, 6 , .. 9 * i 3 x 1*1188 =: 10.886 ,, 10 C.W. of the dilute aolutioa' evolved 10'749 ,, 10 c.cs. ?> Y ? 11.29 Yt 10 c.0s. 9 ) 9 ? 10*868 ,, 10 C.W. ?? 9 , 10*754 ,, 10 c.cs. 9 9 3 ) 10*740 ,, 10 0.CB. ?? ?, 10453 ,, Sarqde B, soid u s 10 t'oh., mas slightly acid, contained Na,O and Hal ; 10 c a . left '0066 gram residue.Diluted and acidified as before :- 10 C.W. of the dilute solutiou roquired 15-31 C.W. K,Mn,O, 10 c.cs. ? ? I , 15.22 9 , 10 43.08. ? * 1, 15-22 9 9 10 c.c.9. 9 ? 9 , 15.31 > ? 10 0.w. 9 ) 9 9 16'23 9 , 10 c.cs. ?? 9 , 16.22 $ 9 Average 15-28 c.m. By equation 4, ,. 1528 x 1.007 = 15.387 0.c~. of gas. ? 9 5, .. 15*2S Y 1*1188 E 17.095 ,) 10 c.cs. of the dilutc soliitiou evolvod 17*357 ), 10 C.C8. 9 9 17.034 ,, 10 0.0s. 2 , 9 ) 16.986 ,, 10 c.cs. 9 , ?7 16.944 ,, 20 c.cs. ,> *> 17*134 ), 10 c.09. 16.898 ,, >? ?> The foregoing results tend to show that Kiugzett's equation is the correct one, and this was further proved by employing the iodine re-action. For this purpose, 10 c.cs. of solution of hydroxyl were taken, acidified and diluted, as in the previous ex- periments, to an aliquot part, 5-10 c.cs.of solution of potassic iodide were added, decinormal aodic thiosulphate was then run in from a burette, until the colour was nearly dischai*ged; borne starch paste was then dropped in and the titration continued, until on staading for a considerable t h e , the blue colour. did not re-appear. By the equatioas, I2 + ZNa&O, = 2Na -1- + *?O N~I- % 40, 2KI + H.,02 = K.0 i 1 C.C. of decinoml thiasulphate is equal to *0017 gram of H202, and corresponds to the perrnnuganate in ecpation G; therefore to prove this equation to t o the true oiie it isTHE ANALYST. 39 only necessary to show that equal volumes of similar hydtroxyl require equal volumes of the two reagents, and this we find to be practically the case, for- Sample D, diluted as before :- 10 c.cs.of the dilute solution required 15-39 c.cs. 4 Na8,O3 10 C.CB. 9 9 ,, 15.1 ¶ * 10 c.cs. F % ) p 15.29 3 ) 10 c.cs. ¶ ¶ 1 , 15-2 Y 9 10 0.00. 29 ,, 15.3 9 , 10 C.08. 19 ,, 15.1 9 ) Average 15-23 c.cs. Sample B, diluted as before :- 10 cm. of tho dilute solution required 14.4 c.cs. $ Na,S,O,. 10 c.cs. Y, 8 , 14p61 Y * 10 em. 9 , ,, 14-62 ?t 10 c.cs. 9 , 9 , 14’62 $ 9 10 (3.08. ? $ y t 14-62 ¶, 10 c 08. 97 ,, 14.31 9 # Average 14.51 c.cs. These results lead to the conclusion that the re-action with permanganate should be represented thus :- K2Mn2O8 + 5H20g + 3n2s04 = &so, + 2MnSO4 + 8H20 + 50, In addition to the above the action of potassic bichromatein presence of mlphuric acid was tried, in this case half the volume O€ oxygen liberated is derived from the peroxide, perchromic acid being formed as an intermediate step, as the following equation shows :- K,Cr,O, + 3H202 +H,SO, = &SO, + Cr,O, + 4 HzO + 0 { cl.,O, + 8H,SO, + Cr, (SO4)$ + 3H,O + q02 In practice we find that hydroxyl may be quickly and accurately estimated volumetri- cally by means of decinormal potassic permasganate, the termination being well marked even by artificial light; that the method with iodine and thiosulphate is not to be recom- mended where rapidity is of importance, bemuse the action is liable (even in presence of much free acid) to become exceedingly slow towards the last, and as the change appears suddenly and only after some time, there is a danger of taking it as complete prematurely .The method of measuring the volume of gas is liable to several objections ; it requires more manipulation and longer time for completion, involves more calcula- tion, and there is always the liability of an unseen leakage taking place ; also if an excoss of pemanganate be added, the gas evolved on standing may be in excess through decomposition of the acidified permanganate, whilst if sufficient time is not given, the fluid in the flusk remains auper-saturated with gas : this, however, may be overcome by frequent gentle shaking, or if the receiver is large enough to contain the heated gas by boiling. We are of opinion that this source of error accounts for the discrepancies in40 THE ANALYST. our results, but believe that they are not sufficiently great to invalidate the deduction drawn.Collecting over water is inadmissible, as no proper correction can then be made for solubility. Other methods are (1) adding an excegs of standard arsenious acid solution, and measuring the excess with iodine ; and (2) the titration of the sample upon a weighed quantity of ferrouw ammonium sulphate, using potassic f erricyanide as an external indi- cator ; in our hands the latter gives resulte a little low, as will be seen from the following figures, which are averages of 8 or 10 closely agreeing experiments. One C.C. of hydroxyl acidified and dilutedrequired 30.53 c.cs. of E2Mn208 = *0519 gram €GO2. 1 C.C. of the same sample had 40 c.cs. As,O, solution added and required 9.63 C.C.% iodine, therefore 40-9.63 = 30.37 x -0017 = -0516 gram H202. 1 C.C. of the same sample was diluted to 10 i ~ c s . with water containing 6 per cent. of H,S04 (1 : 3). 05125 gram of the ferrous salt required 4-8 c.cs. of this solution, there- fore, from the equation :- 2FeS04A~S0,, 6Aq + H202 + H2S0, = Fe,(SO,), + Am,S04 + SKO \- u then ?4 x7i: ,” zi252 = -0462 gram H,O, 784 = 34 With reference to the term volume strength,” it is noticeable that dealers have The total volume of gas liberated by the action of potassic perrnanganate from unit volume of hydroxyl solution being the most lucid and definite explanation that we received. If this were the case it would give to most of our samples nearly double the strength they were stated to be and may therefore be at once discarded, it not being the usual practice in commerce to understate values. somewhat vague ideas as to its signiiicance.Evidently the volume of oxygen available in unit volume of hydroxyl solution only ia the proper meaning of the term. We may say that the samples examined were procured from firms of good repute, and were sold to us as being of fair commercial quality, and nearly approximating to the strength stated. It may, we think, be fairly anticipated that as the value of hydroxyl becomes more widely recognised, it will be produced at n cheaper rate, and become more extensively used, whilst, owing to its tendency to deteriorate, analystsmay be called upon to under- take its estimation more frequently than has been the case hitherto. DISCUSSION. MR. KINGZETT, after remarking that a full account of his investigation into the same subject ia given in the last edition of Xzctton’s Volzcmetrio Alzalysis, said that if in the titration by sodium thiosulphate, a great excess of sulphuric acid be employed, and particularly if the temperature be very slightly raised, the slowness of reaction ordinarily experienced disnppearcd, and the whole was over in two or three minutes.THE ANALYST. 41 He had constant occasion to make such determinations, and he now employed this method to the exclusion of all others, because, having tested it against all other processes, he knew that it mas the most accurate. The essential point was to have a very large excess of sulphursic acid, and he employed equal volumes of that acid, and of the peroxide of hydrogen solution. In reply to a question as to his exprience of the peroxide of hydrogen solution by various makers, he stated that what professed to be of ten volume strength, usually only showed seven or eight volumes, and he had met with cases of professedly twenty volume solutions which contained only six volumes. The per-centage of peroxide of hydrogen, evidently, depended to a great extent upon the age of the solution, and the conditions under which it had been kept.