CHrlPilUN OK h NEW SYXTHESZS OF FORillIC ACID. 133 1X.-On a new Synthesis of Formic Acid. By ERNESTTHEOPHRON CHAPMAN. [Contribution from the Laboratory of the London Institution.] FROMa careful consideration of the results obtained by Mr. Thorp and myself in our investigation of the action of VOL. xx. I4 CHAPMAN ON A NEW SYNTHESIS oxidizing agents on organic bodies it appeared to me difficult to account for many of the reactions on the assumption that nascent oxygen was the sole agent in effecting the change. Thus to take a very simple case acetate of ethyl yields by oxidation two equivalents of acetic acid. In this case we have the same amount of hydrogen in the products obtained as in the substances operated upon. There are only two hypotheses possible in this case ; either the ethyl has given up a portion of its hydrogen to the residue of the acetic acid and has then itself appropriated two equivalents of' oxygen or the acetic ether has been decomposed by the assimilation of water and the substitution of' oxygen for hydrogen which amounts in point of fact to the action of hydroxyl.The assumption of the existence of hydroxyl in the oxidizing mixtures described in the paper before alluded to is of course an impossibility for hydroxyl is immediately decomposed by these liquids. It is we know difficult to convert water into peroxide of hydrogen but I am at a loss to understand t,he decomposition of bichromate of potash by concentrated sulphuric acid and heat uidess upon the assumption that hydroxyl is formed and at once decomposed by the excess of chromic acid present.This may appear a somewhat strained hypothesis. In order to give it weight it was necessary to find some instance in which an unequivocal addition of hydrogen actually took place in such an oxidizing mixture. The following synthesis of formic acid furnishes such an instance ; and I may remark that it was not undertaken with any idea of proving the truth of the foregoing hypothesis though had it not been for that hypothesis I should in all probability neither have carried out the investigation nor have put a correct interpretation on the results obtained. I wished to know whet'licr an acid solution of permangsnate had any action upon carbon in the &ee state ie.charcoal lamp- black &c I found that it did act upon it though but slowly unless the solution were very concentrated and contained much acid. Still there was no question but that action and very considerable action too took place provided sufficient time were allowed. Crystallized permanganate of potash was dissolved hi dis-.tilled water and a8 much sulphuric acid added as would Serve to liberate the permanganic acid. Lamp-black which had been intenrJely igsited waB then added *and the mixture boiled. OF FORNIC ACID. After some hours’ boiling the solution had changed to a brownish-black colour. On standing it became clear. The colour of the clear liquid was then seen to be very faintly pink. A few drops more sulphuric acid were added and the mixture distilled.The distillate was tasteless or nearly so and quite colourless but on adding a drop of ammonia and a little nitrate of silver and boiling a brown coloration was obtained. This constitutes the well-known test for formic acid. Now as even after the most intense ignition lampblack is said to retain traces of hydrogen-a statement which I am utterly unable to verify-I thought it advisable to employ some form of carbon which should be free from this objection. I tried pasBing car- bonic acid over ignited sodium but the yield of carbon froill this experiment is deplorably small. The mixture of oxide of sodium and carbon was dissolved in distilled water. [N.B.-The distilled water employed in this and all the fol- lowing experiments had been re-distilled slowly from perman- ganate.The vessel in which the distillation was conducted as well as the interior tube of the condenser and every other piece of glass apparatus used had actually been made red-hot so that it was free from all suspicion of organic matter No cork india-rubber nor any form of organic matter was allowed to touch the interior of any of the vessels.] The carbon gradually settled to the bottom the alkaline solu- tion above it was poured off and the carbon washed by decanta- tion with hot distilled water. It was then operated upon in the manner already described very minute quantities of per- mailgallate and sulphuric acid being employed. The operation was conducted in a digestion tube in the oil-bath.The tube was opened a little sulphuric acid added and a small portion of the liquid distilled off. But little of the carbon had disap-peared. The liquid in the tube was poured 06more distilled water added this again poured off permangauate of potash and sulphuric acidagain added and the process repeated. This was done six times. The distillate obtained in this manner was rendered alkaline by a drop of solution of potagh evaporated down to n uery small bulk and the silver test for formic acid applied. It gave a very considerable precipitate. The carbon used in the next experiments wa~ obtained fisonz hi-sulphide of carbon by the action of sodium. These two sub-stances when gently heated together yield aulyhide of sodium L.2 CHAPMAN ON A NEW SYNTHESIS and a substance which I take to be pure carbon.It was washed in the manner previously described and ignited in a covered platinum crucible. There wad something more than a gramme of it. It was treated in precisely the same manner as the carbon obtained from carbonic acid had been and the distillate obtained from it also gave the characteristic reaction with ammonio- nitrate of silver. Still no quantity of formic acid had been collected. Reactions had been obtained which rendered it highly probable that formic acid was a product of the gradual oxidation of carbon but the proof was still far from complete. The question in fact resolved itself into this apparently simpler one where can we obtain pure cazbon not in the state of graphite but in the amorphous condition? I believe that it may be obtained by simply igniting lamp black; but I fear most chemists would regard this as a delusion.I therefore mixed finely divided lamp-black with a small quantity of nitrate of potash insufficient to burn more than half of it. This mixture was heated in a platinum crucible. It deflagrated. A portion of the carbon of course remained unconsumed. This carbon I hope may be regarded as free from organic matter; if not I despair of finding any. The carbon was washed out of the accompanying potash-salts with distilled water and dilute sulphuric acid and then treated in the manner previously described. By several operations nearly twenty grammes of it were obtained. These were di- vided amongst five digestion tubes ; great care is necessary in these experiments in apportioning the acid to the permanganate.The solution must be perceptibly but not LIiore than perceptibly alkaline at the close of the operation. If too much or too little acid is employed no formic acid whatsoever is produced. This I have repeatedly verified to my cost. It is better that the liquid should be a little too alkaline than too acid. No advan-tage Whatsoever is gained by using large quantities of perman- ganate. For instance to four grammes of carbon two deci- grammes of permanganate of potash and a corresponding quantity of sulphiiric acid may be added apparently with exactly the same yield of formic acid as if only half the quantity were employed; in fact three of my tubes were always charged with about twice a.s much permanganate as the other two.Ths same number of operations were performed with each lot of carbon viz. eight and as will be seen below the amount of formic acid OF FORMIC ACID. obtained from the two tubes was almost exactly two-thirds of that obtained &om the other three. These operations extended over a considerable time-in fact I was about six days engaged in charging these tubes and dis- tilling from them. The product of two days’ work was employed in obtaining satisfactory qualitative tests with oxide of mercury and amrnonio-nitrate of silver. I obtained the reduction of both these substances. The products of the other four days’ work were devoted to analysis.About three-fifths of the total product (less than a decigramme) was employed in making a combustion that is to say the barium-salt obtained from the distillate was so employed The remaining two-fifths also converted into a barium-salt were employed in determining the saturating capacity of the acid. Combustion was performed with chromate of lead. From the barium determination the following numbers were ob-tained :-Substance taken.. 0-1402 Ba,SO found.. 0.1428 Therefore.. ...... 59-89 % Ba. By combustion the following numbers were obtained :-Substance taken. 0.2052 barium-salt. Found .......... 0.0784 CO and 0-0165 H,O ; Therefore ...... 10.44 % C. and *89%H. Theory. CHBa02. Found C 12 10.57 10.42 H 1 0.88 89 Ba 68.5 60.35 59.89 0 32 28.20 - - -I 113.5 100~00 It appears therefore beyond all doubt that formic acid may actually be obtained by the action of permangnnic acid upon carbon.The process is difficult in the extreme and little more than traces of the acid are obtained. It is only under the cir- cumstances here specified that it is obtainable. We require free permanganic acid to act upon carbon but a trace of potash or some alkali and not more than a trace must be present. imagine that a comparatively large quantity of formic acid k~ formed and destroyed dnring the process.