THE ANALYST. 225 _ _ _ _ ~ - - MONTHLY REOORD OF GENERAL RESEDCHES IN ANALYTICAL CHEMISTRY. ON THE DETERMINATION OF UREA.-BY J. I?. EYlcu.N.--Rec. trav. Chimie. 3,125-136. TKE author acts upon 10 C.C. of the urea solution (containing about Q per cent.) with 50 C.C. sodium hypobromite5 C.C. Br and 150 gim. Na to the Iitre) and 10-15 C.C. sodium hydrate. The mixture is boiled until (5 C.C. have distilled over ; and the evolved nitrogen is collected in a graduated tube over mercury and sodium hydrate containing a little pyrogallic asid; the apparatus is similar to the one lwed for the estimation of nitricacid by means of ferrous oxide. According to the author's experiments, a mixture of 50 C.C. alcoholic broinine, 10 C.C. sodium hydrate, and 20 c.c. water contain 0.5 C.C. dissolved air, and he therefore deducts this amount from the observed volume of nitrogen; the urea calculated from the difEerence is too lorn, and has to be corrected by multiplying by gives 15-30 C.C.nitrogen. 100 /100.4.4L, In analysing urine, the latter must be diluted to sush a strength that 10 C.C. DETERMINATION- OF SILIUA IN IRON AND STEEL.-BY HERB VON JUPTNER.-Oesterr. Zeitschr. f. Bergu. Hiitteum. 32-559. In comnmmioatiofi from the Chemical Laboratory in Neuberg, the author gives a number of anaIyses to compare the following different methods :-( 1) Determination as raw silica (Rohkieselsrture). The iron Wngs were dissolved in strong hydrochloric acid, the solution evaporated to dryness, digested with hydrochloric acid, warmed, and after dilution, filtered, washed, dried, and weighed.(2) By fusing the raw silicawith fusing mixture of carbonates of potash and soda, anddetermininginthe ordinary way. (3) Purification of the raw silica by boiling with strong hydrochloric acid, diluting, fil- tering, and igniting. (4) By treating the weighed raw silica with hydrofluoric acid, evaporating, and weighing. The loas of weight gave the pure silica. ( 5 ) Determination by Brown and 8himer's method. The solution in nitric acid was heated, after adding an equal volume of sulphuric acid until sulphuric fumes were given off. The mean results obtained by the author me the following :-- Nethod 1 2 3 4 5 Raw Iron (HabWesXok. Essefi) 1-68 . a 1.54 .. 1*565 . . 1-50 ,. 1.61 Bessemer Plate , , . . . . 0'049 . . 0.0378 . . 0.0372 . .0.0317 . . 0'0372 The differences among fie fist three methods are easily accounted for by the specialist;. Regarding the 4th method, the reason of the results being low is that the226 THE ANALYST. impurities of the raw silicamere converted into fluorides, mhich are heavier than the corresponding oxides. The last method is especially to be recommended for cases where the manganese is also to be determined (by Volhard’s method). SEPARATION OF ARSENIC FROM TIN AND A.NTIMONY.-BY 3. HmsusMID!r.-Berichte der Chem. Qesell. 14, 1). 2 2 4 5 . T ~ ~ Author did not obtain favourable results with Fischer’s method, (Am. Chem, Pharm., 208, 128), which consists in forming the volatile arsenic tiichloride, by means of ferrous chloride, and distilling. His experiments show that much better results are obtained when the arsenic is distilled in a stream of hydrochloric acid, it being possible to separate all the arsenic in one distillation.The solution to be examined is made up to 250 C.C. with concentrated hyilrochloiic acid, and than distilled in a rapid current of the gas. The volatility of the arsenic is, however, so great that a receiver is not sufficient to retain it ; and the author has, therefore, been obliged to use a modification of Fischer’s apparatus. The receiver is connected with a Woulff’s bottle capable of holding about 900 c.c.; this is filled with either 300 - 400 C.C. of water, or an equal quantity of potash (1.2 -- 1.2 sp. gr.) To prevent overflowing, the delivery-tube, 28 cm. long and 11 rum. in diameter, which clips 10 - 15 em.into the potash. The bottle must be cooled during the operation, as it easily becomes heated. It is not necessary to distil more than 100 C.C. ; all the arsenic is then to be found in the Woulff’s bottle,. but not a ti*ace of tin or antimony. The results are equally good whether an arsenious or arsenic solution be used. The following me some of the author’s eupei.ments :- ARSENIO AND ANTIMONY. Pure metallic Antimony was oxidised with nitric acid, evaporated, and the residue, together with the arsenious acid, washed with hydrochloric acid into the distillation- flask ; the latter was then filled up to a mark, indicating 250 c.c., saturated with hydrochloric acid and distilled. Taken Found DSerenoe. As,O, .. Sb. .. A%03 .. Sb. .. h20, .. Sb. *4960 ..00743 .. 04964 .. ‘0742 .. -0004 ,. *0001 *0967 *. *3596 .. ‘0963 .. ‘3793 .. *0002 .. *003 ARSENIC AXD TIN. (rr) Assenic as Arsenious acid. Taken Found Differenw. &03 .. Sn. .. &O, .. Sn. .. A%O, .. 8 ~ . *1482 .. 01530 .. -1481 .. -1622 .. *0001 *0008 &O, .. Sn. .. Ae205 . + Sn. .* Ae205 , , Sn. ‘1040 ,. *lo60 .. *lo43 .. ‘1048 .. -0008 .. *0002 (6) Arsenic as Axsenic acid. A TEST FOR ARSEXIC.--~~Y H. Hmm.-pharm. centralhalle, xxv. No. 45, p. 537.- IF a small quantity of a solution of sodium thiosulphate be added to a hy&*ochloric aoid solution of arsenic, a yellow precipitate of A+ S3 is obtained. In this way theTHE ANALYST. 227 arsenic can be detached in a solution of 1/16w dilution. The formation of the arsenic sulphide is assured if to 3-5 C.C.of the arsenic solution 2-5 drops of the sodium thio- sulpbate be added. By warming (to 80"-90" 0.) it may be obtained free from, or with very little, sulphur, so that its yellow colour is not hidden. QUANTITATIVE ANALYSIS BY ELEBTROLYSIS.-~N the latest number of the Beriohte dw Bwrlimw Chemischelz Gw.ZZsehaft is a long and interesting paper by Alex. Classen on Electrolytic Quantitative Analysis. The author first describes the process in general; and gives a number of methods for the separation and estimation of the different metals. A short abstract of the paper will doubt- less be interesting to English readers; for the author maintains (B.314. 2771) that the methods are simple and rapid, and allow of even greater accuracy than the ordinary gravimetric ones.The batteries used are either galvanic cells (Meidinger, Leclanch6, or Daniel's) or thermo-electric elements. The Meidinger, which supplies a constant current for a considerable time, can only be used in isolated cases, such as the precipitation of copper, bismuth, and cadmium, as the current is too weak for a quantitative separation of most metala from their double oxalates. The negative electrode, on which the precipitation takes place, is a thin platiaum dish, weighing about 35-37 grms. 19 cui. in diameter, 4.2 cm. deep, and holding abont 225 C.C. water. It is absolutely essential that the dish be perfectly clean and free from fat before use; or else the precipitated metal wilI not adhere to it. Dishes which have, in course of time, become rough and scratched cannot be used.DETERMINATION OF COPPER AND CADMIUM. These inetals are separated out quantitatively from their double ammonium oxalate salts, To obtain a sufficiently weak current two Bunsen elements, in compound circuit (so as to act like one cell), are used. Froin 10-12 hours are required Tor the separation of about 0.15 grrn. Cu or Cd. The end of the reaction may be detected by testing a drop of the copper solution with a fresh solution of potassium ferrocyanide. SEPARATION OF COPPER FROM IRON. The author used iron-alum and cupric sulphate in his experiments. To the solution of the two salts ammonium oxdate is added in excess ; it is then electrolized as above, To determine the iron in the solution free from copper, a few grammes of ammonium ovalate are added, and the solution electrolized with two Bunsen cells, Copper is separated from nickel, cobalt, magnesium, aluminium and phosphoric acid in the same way.DETERXINATION OF ANTI MBNP, Antimony can be precipitated in the metallic state from a cold solution, containing ammonium sulphido in c~ccss. Sundry slight precautions have, however, to be taken ; the ammonia sdphide must contain neither free ammonia nor polysulphides ; and the antimony must not exceed 0.2 grm. To ascertain whether. the reaction be complete, the dish is tilted so that the liquid comes into contact with a fresh surface of platinum j if, after a quarter of an hour, the surface still remain clean the antimony is all precipitated,228 THE ANALYST. DETXRMIXATION OF TIN. To the neutral solution, ammonium sulphide is added, it is then conaiderably diluted with water and electrolized with two Bunsen cells.DETERMINATION OF PLATINUM. The platinum salt; is dightly acidulated with sulphuric or hydrochloric acid (or ammonium oxalate is added), and electrolized while gently warming. It is best to use only one Bunsen cell, for the separation takes place too rapidly with two. The author adds that the inaccuracy of the determination of potassium as potassium platinic chloride is notorious ; and therefore proposes for accurate determinations of potassium, ammonium and nitrogen the precipitation of platinum by electrolysis of the double salts, especially as its separation requires less time than that requisite for drying the platinum compounds. SEPARATION OF FRON COBALT. To determine both metals, the solution of the double oxalates is electrolized by Bunsen’s elements. A few c.c of a potassium oxalate solution (1.3) are added, and, according to the quantity of the substance taken, 2-4 grms. ammonium oxalate ; the whole is then warmed and electrolized. The operation requires from 3-5 hours. The iron and cobalt having been weighed together, they are dissolved in dilute sdphuric acid, and the iron titrated with permanganate solution. To compensate for the colour of the cobalt sulphate, nickel sulphate is added. Iron and nickel are determined in the same may. By electrolysis of the double oxalates. The results are only good when the zinc is less than one-third of the iron; for if more be present, it re.%ssolves. The author gives a large number of results which have been obtained, With the elecholytic methods, in his laboratory ; to judge from these, the process certainly deserves all the praise he bestows upon it. SEPARATION OF IRON FROM ZINC. F. H. H. Bonn, 2 1 st November.