OF CATALYTIC ACTION.

A. A. NOYES AND G. V. SAMMET.

Received March 11, 1903.

INTRODUCTION.

THE experiments to be described in this article were devised as an accompaniment to two lectures upon the subject of catalysis.1 It has been decided to publish them, as it is believed that the series as a whole may be of value in connection with lecture courses on theoretical chemistry, and that some of the separate experiments might be introduced into courses on inorganic and organic chemistry.

The experiments are presented in such a manner as to make their preparation and performance as easy as possible for the lecturer. As this involves the enumeration of many details, those who desire to obtain only a general view of the experiments here described are recommended to read, under each experiment, only the paragraphs entitled "Catalyzer", "Reaction Catalyzed” and “Observations", omitting those designated "Preparation" and "Experiment".

In accordance with the proposal of Ostwald, we understand the term catalysis to signify the acceleration or retardation of a chemical reaction by substances which themselves undergo no permanent change as a result of their action.

For convenience of consideration we distinguish the following important types or classes of catalytic agents:

1. Carriers; 2. Adsorbent contact agents; 3. Electrolytic contact agents; 4. Water; 5. Dissolved electrolytes; 6. Enzymes; 7. Inorganic colloids.

I. CATALYSIS BY CARRIERS.

By carriers are understood catalytic agents which are known to accelerate reactions through the formation of an intermediate compound with one of the reacting substances. Although it is

1 Delivered before the North-eastern Section of the American Chemical Society and the Society of Arts of the Massachusetts Institute of Technology.

probable that some of the other types of catalytic agents (for example, enzymes) are in reality carriers, the term is here confined to those agents which are known to be such.

The experiments here described illustrate the action of carriers in the three states of aggregation, gaseous, liquid, and solid.

The suggestion of Wagner1 that carrier-actions be designated pseudo-catalyses, thereby implying that they are not true cases of catalysis, seems to us an unfortunate one. There has always been a tendency to attach to the term catalysis a mysterious significance, which would be continued if the term is still to be confined to unexplained accelerating actions. The advantage of Ostwald's definition is that it is a concrete, experimental one, having no reference whatever to the way in which the acceleration is brought about.

Experiment 1.

=

2SO3.

Catalyzer.-Nitric oxide.

Reaction Catalyzed.-2SO, +02

Preparation of the Experiment.-Graduate roughly, a long, narrow bell-jar of about 500 cc. capacity by marking lines upon it with a blue pencil at points corresponding to "/15 and 11/15 of its total volume measured from the closed end of the jar. Rinse the jar with water so that the inner sides of it will be wet; fill it with mercury, and invert it over a long narrow trough, also filled with mercury, and having a deep longitudinal groove in the bottom. Introduce sulphur dioxide into the jar until the meniscus falls to the upper mark; then introduce, by means of a bent tube, enough water barely to cover the surface of the mercury. Connect the bent tube with a gasometer or cylinder of oxygen by means of a rubber tube. Fill two short, wide test-tubes with mercury, and invert them over the trough. Introduce into one of these tubes a volume of nitric oxide equal to 0.1 of the total volume of the belljar, and into the other tube one-half this amount of nitric oxide.

Experiment. Introduce into the bell-jar oxygen from the gasometer or cylinder, until the mercury meniscus falls to the second. mark. Place the mouth of the test-tube containing the larger amount of nitric oxide in the groove beneath that of the bell-jar, 1 Ztschr. phys. Chem., 28, 78.

and tip the tube until the gas has passed into the jar. After the mercury has nearly stopped rising, introduce in the same way into the jar the nitric oxide gas in the second tube.

Observations. No change occurs on adding the oxygen to the sulphur dioxide. When the nitric oxide is introduced, the gas reddens and begins to contract and become filled with white fumes. A white deposit (nitrosylsulphuric acid) soon forms on the sides of the jar. The contraction nearly ceases after 30 to 40 seconds, but becomes rapid again when the second portion of the nitric oxide is introduced. The volume finally becomes constant at about 0.2 of the total volume of the jar.

Experiment 2.

Catalyzer.-Sulphuric acid.

Reaction Catalyzed.—2C2H2OH= (C2H2)2O+H2O.

Preparation of the Experiment.-Connect a 500 cc. distilling flask with a Liebig condenser which is fitted with an adapter delivering into a 200 cc. graduate. Place in the flask 135 cc. of concentrated sulphuric acid, and add slowly 75 cc. of alcohol. Insert a 2-hole rubber stopper holding a thermometer and a 150 cc. drop-funnel, both of which reach nearly to the bottom of the flask. Fill the drop-funnel with alcohol, and, just before the lecture, heat the liquid in the flask to 140°-150°; then allow the alcohol to flow slowly into the flask at such a rate that the distillate drops rapidly into the graduate.

Experiment. Add to the ether which has collected in the graduate 2 cc. of powdered potassium carbonate, and shake. After the layers have formed pour the top layer into a 200 cc. graduate which contains 75 cc. of water, and shake.

Observations.-The alcohol is continuously converted to ether, which comes over in the distillate and holds the water which is also produced by the reaction in solution; but on adding the potassium carbonate the distillate separates into two layers consisting of about 5 cc. of water to 100 cc. of ether. On pouring the upper layer into water, it does not mix with it, showing that the distillate is mainly ether, and not alcohol.

=

Reaction Catalyzed.-C.H. + Br, C,H,Br+ HBr.

Preparation of the Experiment.—Support a 250 cc. distilling flask upon a lamp-stand and connect its side-arm with a funnel whose mouth dips just below the surface of a caustic potash solution. Place in the flask 4 cc. of bromine. Provide a cork stopper for the flask, a long-necked funnel, a small wash-bottle, like that used in Experiment 2, containing strong ammonia, 30 cc. of benzene in a small bottle, and 0.5 cc. of powdered iron.

Experiment.-Pour into the distilling flask the 30 cc. of benzene; then add the 0.5 cc. of powdered iron. Blow ammonia gas from the wash-bottle over the neck of the distilling flask. Finally insert the cork.

Observations.-No action occurs between the benzene and bromine alone, but a vigorous boiling up and great clouds of white fumes are observed as soon as the iron is added.

Experiment 4.

Catalyzer.-Aluminum chloride.

Reaction Catalyzed.-C.H.+CH2COC1=C,H,COCH,+HCI. Preparation of the Experiment.—Place a 250 cc. distilling flask in a clamp on a lamp-stand. Connect the side-arm with a funnel that dips just beneath the surface of a potash solution. Pour into the flask 10 cc. of acetyl chloride. Provide a cork stopper for the flask, a long-necked funnel, 50 cc. of benzene in a small bottle, 10 cc. of powdered sublimed aluminum chloride in a corked test-tube, and a small wash-bottle of strong ammonia with a rubber syringe bulb attached to the longer tube.

Experiment. Pour into the flask through the funnel the 50 cc. of benzene, then add the 10 cc. of aluminum chloride. Blow from the wash-bottle ammonia gas over the mouth of the flask, and finally insert the cork.

Observations. No action occurs between the benzene and acetyl chloride alone, but a vigorous effervescence and copious evolution of white fumes occur soon after the aluminum chloride is added.

Experiment 5.

Catalyzer.-Platinum foil.

Reaction Catalyzed.-2CH,OH + O2 = 2CH2O + H2O.

Preparation of the Experiment.-Pour into a 300 cc. beaker a layer of methyl alcohol 1 cm. deep. Cover the beaker with a perforated watch-glass in whose perforation is a cork stopper from which a star made of platinum foil hangs down by a platinum wire 2 to 3 cm. above the surface of the alcohol.

Experiment.-Ignite the methyl alcohol vapor in the beaker by applying the flame of a burner to it, and raise one side of the watch-glass a few millimeters by inserting a bit of wood or rubber tube.

Observations. The platinum star glows brightly when the amount of air admitted to the beaker is properly adjusted.

2. CATALYSIS BY ADSORBENT CONTACT AGENTS.

By adsorbent contact agents we understand solid substances that accelerate reactions by the adsorption on their surfaces of one or more of the reacting substances. Whether the acceleration is due to an increase in the concentration of the reacting substances, or to an activation of them, or to a chemical combination constituting a carrier action, is not thereby taken into consideration.

The experiments to be here presented refer mostly to gaseous mixtures, but include one dissolved substance (hydrogen peroxide).

Catalyzer.-Platinum.

Experiment 6.

Reaction Catalyzed.—2xNH,+y02 = 3xH2O + ≈N2+wNO. Preparation of the Experiment.-Place in a wide-necked bottle of about 250 cc. capacity, 75 cc. of concentrated ammonia-water (sp. gr., 0.90). Insert a delivery tube, which is connected to a tank of oxygen, so that it dips below the surface of the ammoniawater. Wind one end of a platinum wire (about 0.5 mm. diameter) around a match, leaving the other end so long that, when the match is supported across the mouth of the bottle, the end will be about 1 cm. above the surface of the liquid.