Prof. Bunsen on the Radical of the Cacodyl Series. 49 WIL. On the Radical of the Cacodyl Series of Compounds. L3y Professor BUNSEN Marbarg. of Read December 21,1841. 1. Isolation of Cacodyl. SOME of the cacodyl compounds have the remarkable pro-perty of being decomposed by metals. When sulphuret Professor Bunsen on the Iiudical of cacodyl is heated in contact with niercury in a large vessel to 200' or 300' C. the mercury becomes covered with a stra- tum of sulphuret of mercury without any apparent disen- gagement of' gas. The fluid which condenses in the vessel gives off' fumes and takes fire of itself in air if the heat has been continued long enough and the temperature sufficiently high. This process is however not available for the exhibi- tion of cacodyl as the mercury only acts upon the sulphur compound of cacodyl at a temperature at which cacodyl already begins to be decomposed.Bromide of cacodyl be- haves in the same manner; under similar circumstances a mixture of bromide of mercury and a fluid which fumes in the air is produced :-Kd Br 7 f Kd Hg ,J = XHg Br. When this mixture is boiled in water the bromide of mercury is reduced aiid bromide of cacodyl-is regenerated and giveh off with the watery vapour :-Kd 1 (Kd Br HO H 0. The last reduction alsgtakes $ace at too high a temperature for the exhibition of the radical. The isolation is most easily and perfectly effected by using a metal capable of decomposing water and forming a chloride particularly zinc iron or tin.When tin or any of the foregoing metals is added to anhy- drous chloride of cacodyl the metal is dissolved at a tempe- rature of goo to 100' C. without any evolution of gas. The solution which is at first clear becomes of a dark colour on further solution of the metal. Water separates the pure chlo- ride of tin and leaves cacodyl mixed with a trace of chloride of cncodjl behind :-&I Sn a } ={g;c** As zinc however effects the reduction of the chloride with the greatest facility and as no fiirther decomposition takes place in the chloride of zinc formed I have in my experi- ments exclusively used this metal for the isolation of' the radical. Notwithstanding that the reduction appears so easy still as it is very difficult to prevent subsequent decomposition in repeating the distillation and crystallisation of a substance which is as inflammable as the vapour of phosphorus I think it necessary to enter into fiirther details regirding the method of producing it.Very thin sheet zinc the surface of which has been pre- of the Caeodyl Series. viously cleaned with dilute sulphuric acid and afterwards well washed is cut into small pieces to be employed for this pur- pose. The chloride of cacodyl must be quite free from oxy- gen. By digesting oxide of cacodyl three times over in con- centrated hydrochloric acid a pure substance is procured which does not give off any vapour. 'This chloride milst be allowed to remain in a close vessel with chloride of calcium and caustic potash without being distilled in order to deprive it of any water it may contain and also of any excess of acid.To prevent all access of air in this operation a glass vessel of this description is employed (fig. 1.). At Fig. the opening a a stream of carbonic acid is con- ducted through the vessel with the bulb e to contain the substance to be dried. When the atmospheric air is entirely displaced both ends n and 6 are sealed. When the vessel is re-quired for use the point a is broken and at- tached by a caoutchouc tube connected to an air-pump; the point b is then broken and put under the surcace of the chloride of cacodyl; the latter is sucked up into the apparatus and then immediately closed I will call this the drying apparatus.The reduction and distillation is carried on in a somewhat similar manner in an atniosphere of carbonic acid in a closed vessel (fig. Z.) the bulb a being the distillation tube and the bulb b the receiver. Fig. 2. The whole apparatus being pre- viously filled with carbonic acid the chloride of cacodyl is sucked into the bulb n also containing the zinc. The open end of the vessel is then immediately closed with the blowpipe. It is exposed to the tem- perature of 100' C. for three hours in a water-bath. The zinc is readily dissolved without any evolution of gas and the solution becomes of a dark colour. On cooling to 50' C. large cubic crystals are formed which are redissolved by heating. These crystals are probably a combination of chloride of zinc and chloride of cacodyl.When the zinc is no longer acted upon at 103' C. the contedts of the bulbs appear converted into a dry mass of salts which upon an increase of temperature to 110° or 120° C. melts into an oily-like Professor Bunsen on the Radical liquid. After the whole apparatus is warmed the point of the receiver b is opened under cold water previously boiled. Upon the entrance of the water upon the cooling of the apparatus it is again sealed and the water is con- ducted into the distillation bulbs. After a short digestion a solution of chloride of zinc is formed the zinc in excess remaining with a clear surface and leaving the radical at the bottom as an oily liquid. This liquid is then trans-ferred into the drying apparatus aid when perfectly dry is sucked up again into the distilling apparatus and digested for a short time with clear zinc by which means a small quan- tity of chloride of zinc is formed.It is then distilled and comes over as clear as water. At a temperature of -6' C. large prismatic shining crystals are formed. After two-thirds of the solution has crystallized the remaining solution is again distilled and this is repeated three times over. The solution is finally put into a tube filled with carbonic acid. The analysis of this liquid was conducted in the usual manner with oxide of copper. The arsenic sublimed in fine crystals in the back part of the tube without the formation of any arsenical copper or any arsenical salts.The quantity of arseiiic was ascertained by weighing the tube before and after heating. The analysis gave the following results :-1. 2. Substance . . . . . . 0*620gr. 0.500 gr. Carbonic acid . . . . 0*500 0.402 Water. . -. . . . 0'306 0'200 Tube before heating. 62.681 60-670 ... after heating . 61.869 60.020 The composition of this radical is therefore Calculated. 1. 2. Carbon 4 equivalents 23-15 22.30 22.23 Hydrogen 6 Arsenic 2 ... ... 5-67 71.18 5'48 71.29 5*33 71. Loss and Oxygen . . . 0-00 0.93 1.44 100' 100. 100- The trifling difference between the quantities found and the calculated quantities arises probably from the impossibility of obtaining this compound free from oxygen. If the results obtained are reckoned in the 100 parts without taking notice of the oxygen the carbon and the hydrogen agree still closer.The quantity of arsenic on the contrary appears rather too much. The facility with which cacodyl can be separated from its compounds by simple substances renders it very of the Cacodyl Series. 53 probable that the oxide might be also reduced by means of carbon as well as hydrogen upon the application of a higher temperature. Dumas's analysis as well as my previous one of the liquor of Cadet renders this supposition nearly certain and fully explains the cause of our arriving at different results. Dumas found as I did also in my first experiments acon-stant excess of arsenic carbon and hydrogen which is ac- counted for by the impurity of the oxide of cacodyl.There was no difficulty in ascertaining the density of the vapour of the liquid as the temperature at which it is decom- posed is considerably higher than its boiling point. Substance ........ 0*2500gramme. Volume measured. ... 55-98 Cbr. Temperature ...... 200' C. Barometer ........ 328'5 lines. Column of oil ..... 38 lines. Col. of merc. at ZoooC. 44.5 lines. This gives the density of 7.101 which agrees as nearly as could be expected with the calculated density viz.-4 volumes of vapour of carbon . 3.3'71 12 ... hydrogen ..... 0-825 2 ... vapour of arsenic .10'367 14363 -2='7*281. The difference of 0.18 in the result obtained is fully ac- counted for by the tension of the mercury vapour in the ba- rometer at the temperature of ZoooC.The agreement of both the analysis and density of the va- pour with the respective calculated quantities is a matter of coiisiderable interest. Berzelius has shown that when a cer- tain density of a gaseous organics1 radical is assumed the relative condensation which the compounds of this radical present exactly agree with those of inorganic or simple ra- dicals. This circumstance has given a weight to the theory of the compound radicals which the law of substitution could not reach. But this in connexion with the phaenomena of substitutions does not advance the idea of organic radicals be- yond the limits of a hypothesis. The proof of their reality is connected with three other conditions viz. 011 their isolation on the direct formation of their compounds and on the actual agreement of the density of their simple elements with their theoretical density.All these conditions are fulfilled in regard to cacodyl it may be isolated it enters into direct combina- tions and it has the density required if the laws of condensa-tion of the inorganic elements are valid for organic bodies as may be observed by the following statement. Professor Bunsen on the Radical Cacodyl ............ 4 vol. C + 12 vol. €1 +2 vol. As= 2 vol. Kd Observed. Calculated. 7.101 7.281 Cacodyl oxide . . . 2 vol. Kd + 1 vol. 0 = 2 vol. Kd 0 7.555 7.833 Sulphuret Cacodyl2 vol. Kd + 1 vol. S = 2 vol. Kd S 7.810 8-39 Chloride Cacodyt .1 vol. Kd + 1 vol. C1= 2 vol. Kd C1 4.56 4.86 Chloride Cacodyl .3vol.KdC1+ 1vol.KdO =4vo1.3 KdCl+KdO 5-46 5.30 Cyanuret Cacodyl . 1 vol. Kd + 1 vol. Cy = 2 vol. Kd Cy 4.65 4-54. This radical possesses the following properties :-It is a clear thin highly refracting liquid very similar to oxide of cacodyl ; it has the same smell but is more inflamma- ble. A glass rod moistened with it immediately takes fire when exposed to the air its boiling point is about 170" C. At -6' C. it crystallizes in large square prisms; if the sub-stance is pure it becomes like ice. It burns in oxygen gas with a pale blue flame and forms water carbonic and arsenic acids which rise in the form ofa white smoke. If the air is not in sufficient quantity for the combustion Erytrarsin is formed and a black stinking mass of'arsenic remains In chlorine it burns with a clear flame and deposits carbon.Digested with hydro- chloric acid and metallic tin it is converted with the appear- ance of various products into erytrarsin. 'I'he same substance is produced by the action of phosphorous acid chloride of tin and other powerful reducing agents. Fuming sul-phuric acid dissolves the radical without combining with it. In the cold a quantity of sulphurous acid is evolved and on distillation it gives oRa substance with an agreeable aethereal odour which appears to be sulphate ofaetherol. 2. Formation of the Compoundsof Cucodylfrom their Radical. The relative condensation of the gaseous compounds of cacodyl and the transformations which they undergo,. give a great degree of probability to the theory of organic ra- dicals which is now rendered perfectly incontrovertible by the power of this radical to form directly the coppounds from which it was separated.The whole series of com-pounds already considered can be formed either in the di- rect or in the indirect way and the conditions under which this happens are precisely those observed with regard to the metals. The indirect action of oxygen as well as the action of most of the oxidizing agents occasions an increase of tempe-rature in the formation of both the oxide and the acid of this radical; and from the first by the action of hydracids we obtain the corresponding combinations with sulphur selenium tellurium chlorine iodine bromine and cyanogen. By the treatment of the so-formed chloride with chloride of copper chloride of platinum chloride of palladium &c.certain dou- of the Cacodyl Series. ble chlorides are formed which I intend to refer to hereafter. When the radical is dissolved in nitric acid and nitrate of silver is added a very considerable precipitate is produced in the form of regular octahedral crystals consisting of a cornbi-nation of the latter salt with oxide of cacodyl which appears to act the same part as constitutional water in salts. A solu-tion of corrosive sublimate occasions the immediate formation of an oxychloride in the form of fine silky crystals composed of 1 atom of oxide of cacodyl combined with 2 atoms of chlo-ride of mercury. Oxidizing agents are not the only bodies which act in a direct manner ; other combinations are also formed in the same way.Sulphur in small quantities is acted upon by the radical being dissolved by it and forms a clear solution- pos-sessing all the properties of sulphuret of cacodyl producing with solutions of oxides of lead and silver sulphurets of these metals and sulphuretted hydrogen with acids. Upon the ad- dition of a large quantity of sulphur a higher sulphuret is formed which is solid and soluble in aether ;from which latter solution it map be obtained in fine crystals. When to cacodyl a solution of chlorine is added its yellow colour is irnmedi- ately destroyed together with its bleaching power; chloride of cacodyl is formed which acted upon by acids gives hydro- chloric acid.All these reactions to which many more might be added of a not less striking nature prove that this radical acts the part in every instance of a simple electro-positive ele- ment and that it is infact a true oigunic metal. 3. Decomposition of the Badicnl. When the radical is distilled with anhydrous chloride of zinc it is decomposed and forms several compounds at differ- ent temperatures. In order to ascertain more precisely the nature of this decomposition pure chloride of cacodyl was digested with zinc in a distillation tube until the whole solu- tion wasconverted into a white mass of salt; the heat was then increased by means of an oil-bath to 200' C. ; a perfectly clear fluid distilled over. When at this temperature nothing further passed over the heat was increased to 220O C.and then to 260' C. It appeared to me dangerous to attempt any further decomposition by increasing the temperature ;the attempt was therefore given up at this point. After the apparatus was cool and the receiver taken off there was no perceptible smell of any gaseous product. The substance which distilled over was again sucked up into a fresh distillation tube containing zinc mid by means of a continued digestion the last traces of chlorine were separated. The di- Professor Bunsen on the Radical stillation was effected by means ot' an oil-bath. When at the temperature of 100"C. nothing more came over the receiver was separated; its contents (No. 1.) were removed into a tube filled with carbonic acid with all the precautions already mentioned and again slicked up into a fresh distillation tube and re-distilled at fiom looo to 170" C.The product (No. 2.) was put up also into tubes. The residue which remained in the distillation tube at 1'70' C. was again for the third time removed into a fresh distillation apparatus and again distilled at from 170' and ZOOo C. without leaving behind any percep- tible residue and forms No. 3. All the three distilled pro- ducts were quite tramparent ether-like very liquid and quite free from chlorine. The first scarcely took fire of itself had a strong ethereal smeI1 and remained liquid at -18' C. The two others were exceedingly inflammable and crystallized at -8' C. in large prismatic crystals like cacodpl.Tested with corrosive sublimate the first gave but little appearance of containing cacodyl; on the contrary the two last appeared to contain a considerable quantity. Analysis gave-No. 1. First Distillation. Substance .......... 0.56 1 Carbonic acid ........ 0*5875 Water ............ 0.3665 Tube before burning .... 80'261 ... after burning ..... '79.310. No. 2. Second Distillation. Substance .......... 0.5403 Carbonic acid ........ 0.5140 Water ............ 0.3145 Tube before burning .... 74.976 ... after burning ..... 74.147. No. 3. Third Distillation. Substance .......... 0.5930 ~~ Carbonic acid ........ 0'4265 Water ............ 0.2635 l'ube before burniiig .... 83.0195 ... after burning .....82*3Z'iO. These results (a repetition of which I think unnecessary as the Weighillg of the tube after burning serves as a check upon them) give the following conipositions :- of the Cacodyl Series. 57 1st distillation 2nd distillation 3rd distillation at 90" to 100" C. at 100' to 170" C. at 170" to 200" C. equiv. equiv. equiv. Carbon. . . 4 28.95 4 26.31 4 19-88 Hydrogen . 6.1 7-26 6.05 6-46 6.1 4.82 Arsenic. . . 1-3 64.31 1.7 67.15 2.55 75-50 I00.52 99.92 100523. It follows from the analysis that this radical on distillation with chloride of zinc undergoes a catalytic decomposition without the separation of arsenic dividing into two or more compounds in which the same quantity of carbon is combined with different quantities of arsenic; a circumstance of much interest as regards the theory of organic radicals.It is there- fore probable that cacodyl like arsenic is a binary radical composed of C H, and that its constituent elements are com- bined in such a manner that the compound of the cacodyl series are repeated in a similar way only of a higher order. The above-described products of decomposition undergo at a teni- perature of about 400Oto 500° C. a decomposition which I an1 in hopes from the peculiarities in the constitution of the radi- cal to direct attention to. When cacodyl or the before-men- tioned mixure of the product of decomposition is heated in a bent retort over mercury the gas of this substance is decom- posed at a temperature little exceeding the boiling point of mer-cury into metallic arsenic and a mixture of a compound of car-bon and hydrogen without the separation of a particleof carbon.This gaseous substance burns with a variegated light flame with cz very slight deposition on glass of metallic arsenic. A solution of sulphate of copper or nitrate of mercury has no action upon the gas however long it may remain in contact. With chlorine over water it takes fire like a mixture of phos- phuretted hydrogen and burns with deposition of carbon producing a red-coloured flame. Mixed with oxygen gas and inflamed by the electrical spark it explodes more powerfully than fulminating ga? and generally breaks the vessel. Eudio-metrical examination of the gas gives the following results :-1. 2. Calculated.Volume of the gas . . . . 1-t 1.5 1.5 ~~ Oxygen gas consumed . . 3.5 3.4 3.5 Carbonic acid formed. . . 2.0 2.0 2.0 These trials exactly agree with a compound in which the combination with the carburetted hydrogen in the cacodyl gives 4 volumes of vapour of carbon 12 volumes of hydrogen condensed into 6 volumes. I was at first induced to suppose that a similar decomposi- Professor Uunsen on the RndicaZ tion of cacodyl took place as in the case of cyanide of mer-cury as the action of this gas with chlorine did not agree with the action of any of the compounds from which this mixture of gases could in any nianner arise; but the uncommon con- densation the essential circumstance in this case appeared little to support this view.I have therefore continued the examination and found that the burning with chlorine arises from the presence of a small quantity of a volatilizable com- pound of arsenic which does not separate from the mixture and which is at the same time the cause of the small stain of arsenic which on burning this gas in oxygen remains on the side of the eudiometer. The true nature of this gas given out by heat from cncodyl is shown hy the action of fuming sulphuric acid. This absorbs nearly one-third and leaves behind an inodorous gas burning pale blue which is not al- tered by chlorine in the dark in the direct rays of the sun however as Melsens has shown of the gas of the acetates and of marshes it is condensed into oily camphor-like odorous bodies in the state of small white radiating crystals.From a eiidiometrical analysis of this gns it appeared to be pure marsh gas. I found From the volume examined ...19-2 Oxygen consumed ........41.1 Carbonic acid formed .......21 *8 There can therefore be no doubt that the carburetted hy-drogen C H, formed on the decomposition of cacodyl at a high temperature is not separated as such but that there are formed under these circumstances two volumes of marsh gas and one volume of olefiant gas viz. C H As = {:t,", C H The examination of the gas not absorbed by the sulphuric acid confirms this view of the question ;as one volume and a half of the pure gaseous mixture which contains one volume of olefiant gas and two volumes (C H,j of ninrsh gas must in fact upon burning with three and a half volumes of oxygen produce two volumes of carbonic acid.Whilst the absence of arsenietted hydrogen and firnee hy-drogen decidedly proves that the first is not to be considered as a constituent element of cacodyl; the conclusion may be drawn at the same time from these appearances of decom-position that if the radical C PI cat] exist independently it is most unstdde and is decomposed much below a red heat. OJ the Cacvdyl Series. Among the products of the decomposition of cacodyl there is one substance which I have mentioned several times aiid to which I have given the arbitrary name of erytmrsin I shall now consider this substance as it is in close connexion with the foregoing substances.I have not hitherto succeeded in obtaining any quantity of this remarkable substance. It is formed as a secondary product in the formation of chloride of cacodyl sometimes in a great and sometimes in a small quan- tity. It is also deposited upon the distillation of oxide of ca- codyl with water. Upon conducting the vapour of cacodyl or oxide of cacodyl through tubes slightly heated this sub-stance is produced in large quantities by an imperfect com- bustion; but obtained in this manner it is always contami- nated with arsenic from which it is impossible to separate it. The substance next made use of in preparing it was obtained in the following manner. About 100 gramnies of oxide of cacodyl was added to con- centrated hydrochloric acid ; chloride of cacodyl was formed and a red flocculent precipitate fell which after distillation of the chloride remains behind in the retort.The precipitate became during the distillation of a thick consistence which increased and became of a darker colour with the appearance of finely divided red oxide of‘iron. After six or eight lloilings with absolute alcohol the substarice was obtained quite pure and free from chlorine. It is necessary during this boiling to protect it from the air and to dry the substance in a vacuum with sulphiiric acid as otherwise it is liable to absorb oxygen slowly. Prepared in this n~aniier erytrarsin is of a steel blue shading into dark red free from smell and without the least appearance of crystallization. It is easily ruliberl down into a red powder which absorbs oxygen slowly from the air with the appearance of the formation of arsenious acid as it be- comes covered with a white powder This decomposition does riot take place until after exposure for several weeks.It is not soluble in alcohol =ether or water-even caiistic potash does not act upon it. In concentrated and not fuming nitric acid it is soluble with decomposition. Red fuming acid occa- sions oxidation with inflammation. Heated in the air it barns with an ash-coloured arseiiical flame without leaving any residue. Heated in a glass tube it gives out vapours smelling of cacodyl and deposits carbon arsenious acid arid a ring of arsenic. The quantity produced from 100 grammes of oxide amounted to a little above 0*,5graninie.From the want of a sufficient quantity of this substance I have only been able to make one analysis which I however trust is sufi-cient :is every precaution was taken to ensure its accuracy. Chrni 3’ec. Mcn7. VOL. I. 1 60 Professor Bunsen on the Radical of the Cacodyl Series. 0'394 gr. of the dried substance was burned with oxide of copper and gave O*1253 carbonic acid and 0'0'74 water. ?'he arsenic was ascertained from the contents of the burning tube. These were dissolved in nitric acid the solution diluted with water and partly precipitated by carbonate of soda. The solution filtered from the copper was perfectly free from arsenic. The precipitate dissolved in hydrochloric acid to which sulphuret of soda was added also produced no preci- pitate of arsenic The filtered solution gave after being boiled with sulphurous acid in the usual manner 0.5191 sul-phuret of arsenic ; of which 0-6333 acted upon by nitric acid gave 0.0528 sulphur and 2.1566 of sulphate of' barytes.The following are the results :-Calculated. Found. c,. . . 305.76 8.73 8.58 H . . 74*88 2.14 2-08 As . . 2820*24 80*56 8 1*56 0,. . . 300*00 8.57 7-78 3500*88 1oo*oo 100~00 The difference of one per cent. in the arsenic found is ac-counted for from a small quantity of sulphuret of copper which was contained in the sulphuret of arsenic which on account of its small amount could not be ascertained. The atomic weight of this substance I have not been able to ascer-tain in a direct way as it does not enter into any direct com- bination; but the probability is from the relation it holds to cacodyl and to oxide of cacodyl that that stated above is correct.I have therefore shown that the radical of the ca- codyl series is converted at a temperature approaching to redness into marsh gas and oil gas which gases map be con-sidered as decomposing products of a non-isolated carburetted hydrogen C Hq. From what precedes it also follows that of three atoms of oxide of cacodyl two atoms are decomposed in the manner described while one atom of erytrarsin is left behind :-3 atoms ofoxide of Cacodyl C, H, AsG0 2 atoms of C H . . . C8 HI =4CH2+4CH C €3 AsGO The rational constitution of this coinpound can only be con- jectured.As cacodyl in combination with oxygen undergoes the same decomposition at a higher temperature as in an un-combined state it follows that erytrarsin may be considered as the oxide of a ternary radical which can be distinguished from cacodyl only by its containing three times as much Mr. warington on Chromic hid in F701iaicArrangements. 6 1 arsenic. The complete examination of such a substance would be attended with great danger and many difficulties.