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A technique for the quantitation of flat-bed chromatograms or electropherograms involving the minimum exposure time necessary for a spot just not to appear on a photograph has been developed. For calibration purposes the minimum exposure time is plotted against the amount of substance spotted. The amount of a substance present in an unknown spot is determined from the minimum exposure time. The procedure is inexpensive, simple and particularly suitable for occasional quantitations.

The use of classical moving boundary electrophoresis in the study of biopolymers has decreased substantially in recent years. Among the reasons for its loss of popularity are the high cost of the equipment, the complexity of the technique, and the large amount of substance necessary for an analysis. Nevertheless, moving boundary electrophoresis remains the method of choice for the determination of the mobility-pH curve of a biopolymer (1), for as pointed out by Kunkel (2) zone methods are incapable of providing absolute mobilities. The present note describes an extension of the capabilities of the moving boundary method to the determination of mobilities of a biologically active principle at very low concentrations and contained within an impure mixture. The procedure in our new method is similar in principle to that used to determine sedimentation coefficients with a partition cell in an analytical ultracentrifuge (3,4). In the latter technique, the quantity of active substance sedimented across a fixed plane in the cell is measured, generally by a specific sensitive analysis of the biological activity on one side of the partition relative to that in the original solution. An analogous procedure is described here for determination of electrophoretic mobilities in a moving boundary apparatus.

A theory is presented for the study of diffusion in heterogeneous tissue-like structures. It is applicable to a common type of measurement in which the change of the amount of substance remaining in the tissue is determined as the substance diffuses from the tissue into an adjacent medium, for instance, Ringer's solution. The main objective of this paper is to obtain a method for the calculation of the diffusion coefficient in the intercellular space and of the permeability coefficients between this space and the cells, based on the type of measurement mentioned above. Although the fundamental ideas upon which the theory is based are applicable to any type of tissue, the formulae derived are limited to the case in which the cells form a flat bundle of parallel fibers. The theory is applied to the experimental results of E. J. Harris and G. P. Burn on diffusion of sodium in the sartorius muscle of the frog. We find that if we know the ratio of the cellular and intercellular volumes of the muscle the ratio of the equilibrium concentrations of sodium outside and inside the cells can be determined. A very simple mathematical analysis of the experimental relation between the amount of substance diffusing out of the muscle and the time of diffusion gives us this ratio. The ratio of the equilibrium sodium concentrations in the case of the sartorius frog muscle is between about 10 and 30, depending on the muscle used. The same mathematical analysis makes it possible to obtain the permeability coefficients of muscle fibers through simple calculations, if their sizes are known. The permeability coefficients for the experimental work mentioned above using sodium are 1.25 to 11.5×10−8 cm/sec for the flow into the fibers and 3.2 to 16×10−7 cm/sec for the flow in the opposite direction. The determination of the diffusion coefficient in the intercellular space is more laborious and yields only an order of magnitude: 10−6 cm2/sec.

‘Trace’ is a term much used in colloquial language; it has many connotations and should not be ‘appropriated’ to denote ‘scales of working’ in chemistry. The concept “scope of analysis” is proposed instead. The quantities “amount of substance”, “mass” and “concentration” are critically considered and it is proposed that more use of a logarithmic presentation of concentration values should be made. The role of the “blank portion” of measured quantities with respect to trace determinations is pointed out; “analytical signal” and “analytical noise” are discussed. Linearization of the “calibration function” and elimination of the blank measures are required for extrapolation of calibration functions to low concentrations. The different calibration methods (σ, α, δ, ω) are presented; the importance of “rating” analysis and “gradual” analyses with coarsened scales is pointed out. The ‘type’ of information, the “informing power” provided by a procedure and the “information required” by the analytical problem are discussed. The “topological structure” of a procedure is shown to be decisive for its applicability to trace determinations. “Selectivity” and “sensitivity” are defined as metric quantities to be calculated from the “calibration matrix” of the procedure. High values of these two quantities are required for ‘trace work’. “Specificity” is mentioned only. Finally some remarks about the “limit of detection” and the “limit of guarantee of purity” are made to clear up common mistakes, made when applying these useful concepts.

A flexible computer program was set up to simulate the kinetics of the amounts of radioactivity and the amounts of substance in various classes of nucleic acids for a generalized biological system. This program works by transferring numbers from registers to other registers corresponding to the amounts of isotope label or the amount of substance moving from one pool or compartment to another for each successive time interval. It is practical to choose the time interval small enough so that the same results are accurately obtained with this type of computation as with the analytical solution for the most realistic and complicated case previously formulated. Much more complicated situations now can be treated with this recursion program and questions of relevance to current molecular biology can be answered. The questions treated in this paper are directed to enteric microorganisms and are as follows. (1) What are the conditions under which a short pulse reflects net synthesis and what are the conditions where it reflects total synthesis? (2) What are the conditions that measurement of intermediate pool specific activity can yield information about the turnover and concentration of unstable macromolecules in the system? (3) How prolonged can a pulse be and still label the species of RNA substantially in proportion to their rates of synthesis? (4) What are the amounts and rates of synthesis and degradation of ribosomal precursors best fitting data in the literature?

A method for calculating accurate Kovats' retention indices, without the need for bracketing every compound in a mixture by two consecutive n-alkanes, is described. In addition, the method makes possible good control of the column conditions. The calculation is done using a FORTRAN program which is adapted to automatic operation and which also takes into consideration the change of retention time with the amount of substance injected.

A systematic investigation of the extinction of flames by fine powders propagating in a tube, carried out on various propagation regimes ranging from uniform, flames to detonations, has shown that each flame is best inhibited by a substance of optimum particle diameter, variable with the flame parameters. Additional chemical specificity can result only after the convenient particle diameter is correctly chosen. This second stage of the inhibition process can sometimes drastically reduce the amount of substance necessary to produce extinction. In the cases where a chemical specificity is noted, alkaline salts appear to be more efficient when decomposition, fusion or volatilization is likely to occur at low temperature.

Radioisotopes can serve as a suitable tool for the study of diffusion in polymers. Two different methods have been used for this purpose: radiometric measurements, which enable us to determine the total amount of substance diffused into polymers and to compute diffusion coefficients, and autoradiographs, which can yield the distribution of substances in polymer and also the local concentration of diffused substances.

It has been recommended to use SI units in clinical chemistry. A consequence of this is that pH is reported as the excess chemical potential (or standard chemical potential) of hydrogen ions with the unit kJ/mol. On the basis of the excess chemical potential of H+ it is possible to calculate the hydrogen ion concentration in the system = the equilibrium concentration of H+ = the concentration of free H+. This quantity must be clearly distinguished from the stoichiometric concentration of H+ = the excess concentration of total H+, which indicates the amount of added or removed H+. The latter quantity with opposite sign has been called the excess concentration of base, but the designation "stoichiometric concentration of H+" seems to be more logical. The general principles for description of a component in a chemical system are based on (1) an extensive quantity (the stoichiometric amount of substance), and (2) an intensive quantity (the excess chemical potential); the product of these has the dimension of energy.

The concentration of a solution is given as the amount of substance dissolved either in 100 g or in 100 ml of the final solution and is expressed as a percentage. In the first case it is a gram-percent solution and in the second a gram-volume solution.

This chapter covers some of the more elementary calculations in A-level chemistry. Underlying most of them is the chemist’s unit of ‘amount of substance’, the mole. It is vital to make a determined effort to master this concept thoroughly, and to see the point of doing so, before going on to the remainder of the book.

This chapter presents some basic definitions of science, matter, and chemistry. It explains the subdivisions of chemistry. The SI system defines a single base unit to measure each of seven quantities such as length, mass, time, electric current, temperature, amount of substance, and luminous intensity. Other necessary units, such as that for volume, are derived from the base units. The chapter reviews the modern units of measurement and a problem-solving method, the factor-dimensional method. With the factor-dimensional method, a unit-conversion calculation, and the calculation needed to solve a problem, can be set up in a single expression. The chapter describes the role of chemistry in coping with the major problems facing mankind.

In addition to serving as a tool with which to calculate formulae and equations from experimental results, the mole is chosen as the standard amount of substance against which to measure heat changes, reaction rate, concentration and so on.

Publisher Summary This chapter discusses the structural considerations of capillary permeability. Capillaries assist the exchange of certain material required by, or detrimental to, the cells of the organism. There is an active convection of a central reservoir of fluid—namely, blood—throughout the vertebrate tissues by way of the vascular system, but it is mainly in the smallest divisions of this system of conduits where the exchange of these materials takes place. The finest tubes measure about 20 μ m or less in diameter and include capillaries and venules. The walls of these vessels are permeable, allowing the exchange of substances across them. Permeability is a physiological phenomenon and is a measure of the rate of penetration of a substance through some sort of barrier. As derived from Fick's law, which describes the movement of material in response to forces imposed upon it, the amount of substance is represented by ds , and it passes through a barrier in time dt . The amount of material passing in any given time is directly proportional to the area of the barrier and to the pressure difference between the two sides of the barrier, but it is inversely proportional to the thickness of the barrier and the viscosity of the fluid.

For the development of simulation models for gas/liquid reactors it is necessary to describe the mass transfer between the gas and liquid phase for pure physical absorption as well as for the case of chemisorption. As classical balancing approaches for the description of absorption and absorption accompanied by a fast chemical reaction lead to completely different equation systems, an a priori decision about the absorption regime is necessary. Depending on time and locus, different reaction conditions may occur within a reactor, so that an a priori decision is not possible. For practical purposes a hybrid model, which accounts for slow and fast chemical reaction conditions in like manner, seems to be an efficient approach. The model presented here, which can be developed from the classical approach with minor modifications, describes both pure absorption and absorption accompanied by a fast chemical reaction, as well as the transition regime. To use this model for a given reaction syst em, a depletion factor must be calculated beneath the classical enhancement factor. The depletion factor describes the ratio of the amount of substance leaving the liquid film unconverted to the amount of substance absorbed from the gas phase. A first implementation of this method was done in the software code BSR, a simulation programme for bubble column reactors.

IN the course of an investigation of certain fractions obtained from liver extract, it became desirable to purify quantities of a few grams of these fractions by electrophoresis. The object was a complete separation between the migrating and non-migrating parts of the whole amount of substance subjected to electrophoresis.

SURFACE densities can be determined from the decrease in concentration and the estimated total area of a large amount of bubbles or drops made to pass through a solution1: this method is not accurate since the amount of substance adsorbed by the bubbles or drops is dependent on the hydrodynamics of the system.

Notwithstanding the fact that much of modern physiology has concerned itself with the maintenance of constancy of the milieu interieur, a definite lag persisted in the study and understanding of those factors regulating the normal volume and distribution of body fluids. Starling, with his rare insight, had early called attention to the fact that such control must exist, 200 and experiments supporting this idea were subsequently reported, 1,8 but the implications of the results—far ahead of the conceptual thinking of the time—fell upon soil unprepared for germination. Historically, several factors contributed to the delayed growth of knowledge of fluid volume regulation. Measurements of body fluid constituents by the standard chemical methods are reported, in the language of chemists, as concentrations, and so accustomed have we become to this method of expression that students frequently find it difficult to associate a normal concentration with a highly abnormal amount of substance in