Alfred Weissler

Sonochemistry: The Production of Chemical Changes with Sound Waves

An extensive survey is made of the chemical effects of ultrasonic waves. Increased understanding of the mechanism of these effects is sought through a consideration of the significance of certain experimental variables such as frequency, intensity, pressure, and temperature. Also considered is the role of cavitation.

The Velocity of Sound in Sea Water

In the sonar detection of underwater objects an accurate knowledge of the velocity of sound in sea water, and its variation with chemical composition and temperature, is desirable. Eight samples of Caribbean Sea water collected at various depths were studied with respect to sound velocity, density, and chemical composition. At both 20° and 30°C the velocities (determined with a 3‐megacycle ultrasonic interferometer) were about 4 meters/second higher than the values in Kuwaharas tables, for which an accuracy of 3 meters/second is claimed. The salinities determined by chemical analysis agreed closely with those calculated from the densities; a slight increase of salinity with depth was noted. In another series of experiments, the sound velocity, density, and adiabatic compressibility were determined over a wide range of concentration for pure solutions of each of the seven salts which are the major constituents of sea water. It was found that the compressibility and sound velocity observed for sea water ag...

Variations of Cavitation Intensity in an Ultrasonic Generator

The amount of cavitation produced in an ultrasonic generator depends on factors such as tank geometry, water height, and continuous‐operation time. Some typical results are presented, which may help to explain the quantitative variability found in, for example, industrial cleaning and biochemical applications.

Some Sonochemical Reaction Yields

Measurements of the yields of some sonochemical reactions show that the number of molecules produced per unit of energy absorbed is several hundred times smaller than the corresponding radiation chemistry (gamma ray) yields. The ratio of the radical yield to the molecular yield in sonochemistry also is smaller than in a gamma‐irradiation reactions, but is approximately the same as in alpha‐particle irradiations.

Effects of Ultrasonic Irradiation on Hemoglobin

Oxyhemoglobin in dilute aqueous solution is rapidly converted by ultrasonic irradiation into methemoglobin, which in turn is gradually destroyed, as shown by the disappearance of its optical absorption peak at 4050 A. Hematoporphyrin similarly suffers partial destruction by ultrasound. On the basis of experiments in various chemical environments, the previous results are ascribed largely to the nitrous and nitric acids produced by ultrasonic cavitation in water containing dissolved air. Adding 0.1 ml ether/25 ml of solution causes the sonochemical change to be from oxyhemoglobin into carboxyhemoglobin, instead of into methemoglobin. Ultracentrifuge studies indicate that ultrasonic treatment of hemoglobin in more concentrated solution also causes some splitting off of the heme from the globin. A comparison of the reported effects of x rays on hemoglobin with those found for ultrasound shows that there are differences as well as similarities. The ultrasonic frequency used was 400 kc per sec, and the acousti...

The Chemical Effects of Ultrasonic Irradiation: Reaction between Carbon Tetrachloride and Water

Intense ultrasonic waves produce interesting physical and chemical effects, such as emulsification, luminescence, and chemical transformations. In an attempt to clarify the mechanism by which ultrasonic irradiation causes chemical reactions in liquid mixtures, a quantitative study was undertaken of the ultrasonic production of iodine in aqueous solutions of potassium iodide which contain some carbon tetrachloride. It was found that the amount of iodine liberated depends greatly on the dimensions and material of the container, but only slightly on the concentrations of potassium iodide and carbon tetrachloride. Frequencies of 400, 700, 1000, and 1500 kc gave varying results, but this is attributed to varying transparency of the test tube rather than to intrinsic frequency‐sensitivity of the process. Although earlier investigators believed that dissolved oxygen is essential, the present work shows that nitrogen or helium serves nearly as well. As the power input is increased, no iodine is produced until cav...

Biochemical Effects of Ultrasound: Destruction of Tryptophan

A sensitive fluorescence method has been used to study the process by which intense ultrasound (400 kcps) destroys tryptophan in dilute aqueous solution. Tryptophan is an essential amino‐acid found in proteins and is closely related to plant growth hormones, to the vitamin niacin, and to the reserpine tranquillizer drugs. It emits a characteristic fluorescence at about 3600 A when excited at 2900 A. Serial recordings of the fluorescence spectrum after successive periods of ultrasonic treatment, made by means of an Aminco‐Bowman spectrophotofluorometer, show that 95% of the tryptophan is destroyed after 24 min under the specific conditions used. The rate of destruction is somewhat slower in argon‐saturated solution, and somewhat faster in oxygen‐saturated solution, as compared with the air‐saturated solution; in all three cases, the reactions rate conforms reasonably well to first‐order chemical kinetics. As the tryptophan is destroyed, a substance with a new fluorescent peak at 4000 A is produced.

A Liquid with Unusually High Sound Velocity

During a study of the effect of molecular structure on sound velocity in liquids, a liquid was found in which the velocity of sound is 3000 meters/second at 20°C, as measured by a 3‐Mc ultrasonic interferometer. Previously the highest value known was less than 2000 meters/second, for glycerine. The new liquid is a viscous concentrated aqueous solution of sorbitol, prepared by heat dehydration of the commercial syrup “Arlex.” Sorbitol was selected for study, even though it is a solid, because its chemical structure is that of a double glycerine molecule. Concentrated sorbitol solutions also show a dispersion of sound velocity with frequency in the megacycle range (reminiscent of the behavior of polyisobutylene as described by Mason) and absorption coefficients many times larger than that of glycerine.

Ultrasonic Investigation of Molecular Properties of Liquids, Cyclic Compounds

The velocity of sound in a pure liquid depends on the chemical structure of the molecules. In order to study this dependence further, the velocity of sound in twenty cyclic compounds at 30°C was measured by means of a three‐mega‐cycle ultrasonic interferometer which requires only 10 cm3 of liquid. These molecules consist fundamentally of rings of carbon atoms having hydrogens attached, in some cases with atoms of nitrogen, oxygen, or sulfur replacing one or two of the carbons. The values obtained lie between 1100 and 1550 meters/second; the accuracy is estimated as ±0.03 percent. Correlation of the results is facilitated by the use of the molar sound velocity R = v13M/d, where v is sound velocity, M molecular weight, and d density. This quantity may alternatively be calculated as the summation of the R increments for each of the chemical bonds in the molecule. In the present work, the average agreement between the observed and the summation values of molar sound velocity was about 1 percent. Therefore, on...

Chemical Reactions Caused by Ultrasound Waves in Liquids

Chemical reactions caused by ultrasound waves in liquids are surveyed, with some attention to recent research abroad, such as that in the USSR. Consideration is given to the mechanism of the effects and the importance of the nature of the dissolved gas. Hemoglobin, amino acids, enzymes, and other biochemical molecules are included in the discussion. Sonochemistry in nonaqueous systems, a new area, is also described briefly.