The need for improved methods for the determination and characterization of the protein components of human blood plasma requires no emphasis. The commonly employed methods for the separation of plasma proteins on the basis of solubility give little detailed information and generally yield poor separations (1). Likewise, the method of electrophoretic analysis, although of unquestioned value, will fail to differentiate between components of widely differing chemical properties and physiological functions if they happen to have the same mobility in an electric field.The present communication describes the adaptation of Method 10 of plasma fractionation developed by Cohn and his associates (2) for the quantitative estimation of certain of the protein and lipoprotein components in small quantities of normal human plasma. The fractionation is carried out at low temperatures using low concentrations of ethanol and of various salts, resulting in the concentration of each protein component

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The Tangent Sphere Model (TSM) is a useful tool for discussing chemical structure at an introductory level. Physical models of the atom's kernel and valence electrons are easily constructed out of various sized Styrofoam spheres. Students can construct and manipulate the models as they seek to understand the basic ideas of structure, geometry, and bonding. Two-dimensional representations can be drawn utilizing circles of various sizes. Charge and symbols are also used to designate the type of species involved.The TSM may be viewed as a "concrete" representation of the Kimball charged-cloud model. It was first discussed in THIS Journal by Henry Bent in a series of articles in the mid-1960's (see bibliography at end of article). The key points of this conceptual model are presented here as a summary of the work done by the participants of the first Dreyfus Institute held during the summer of 1982 at Princeton University under the sponsorship of the Woodrow Wilson Foundation. This article will serve as a reminder of the usefulness of this model especially for beginning students at both the secondary school and college levels. Assumptions and PrinciplesBelow is a list of the assumptions and principles upon which the tangent sphere model is based. Although the general terminology will be familiar to most readers, it is presented here to complete the general picture of the model. Atomic kernel. The kernel of an atom is a spherical region containing its nucleus and all nonvalence, inner electron pairs. Its charge is always positive, since the number of protons in the nucleus always exceeds the number of inner electrons. Hydrogen is unique in the fact that it has but one proton and one electron and therefore contains no "inner electrons" as in other atoms. It is represented by its nucleus and a one-electron sphere surrounding it, a protonated sphere.Valence electrons. The valence electrons are those found beyond the kernel. Valence electrons are available for chemical bonding.Pauli Exclusion Principle. Because of the Exclusion Principle, no more than two electrons may occupy the same region at the same time, thus limiting the charge on any electron sphere to one or two negative charges.

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Lettersware 1995, 8B, No. 1) aimed at helping students to ask the questions and find the answers themselves.The problem becomes overwhelming, I think, when one has to deal with a large class of students who are variously motivated. You can't tell them to sink or swim in today's world. But perhaps materials could be produced that would enable a self-selected subset of students to emphasize learning rather than assimilation.Beginning with my high school geometry class, which was the first time I actually felt myself using my mind to wrestle with questions that had no pat answer; later with an inexplicable desire to master complex equilibrium calculations beyond those in the text; then struggling with my thesis research; still later during the writing of my textbook-such experiences convinced me that learning is a do-it-yourself activity. As crusty Andy Rooney once put it: "We don't need better teachers-we need better students." (calculated from data in the NIST collection [2]), yielding an error of nearly 20%. The authors could have learned this error from me in my first two decades of teaching. It is a bitter truth that we hand on errors from generation to generation and our profession has no mechanism to correct them. Professional research projects are based on fallacy as a result of our teaching. Literature Cited *We do make the assumption of no ion pairing in solution, as Hawkes points out. In fact, we addressed, albeit only briefly, that an error introduced by ion pairing exists in this system. The reported values of K°s p obtained by the students are about 20-25% from the literature value. Students nearly always obtain a high result, which leads to lecture discussion of errors due to ion association when performing calculations involving solubility. David B. GreenNatural Science Division Pepperdine University Malibu, CA 90263 * Has Chemical Education Reached Equilibrium?Your piece on the possible equilibrium nature of education is most thoughtful and (should be) provocative ( J. Chem. Educ. 1997, 74, 613). I think your editorial should be used as a rallying cry for a CHED symposium on ideas for, well, increasing the value of K eq . A plethora of papers has been presented over the years showing how novel teaching has been implemented, but not many really address the basic question of shifting responsibility to the learner.In my last several years of teaching I came to realize how minimal my teaching effort (which was enormous, from my viewpoint) was, compared to the importance of student initiative in their own learning. KinWORKS In regard to your June editorial in JCE concerning the state of chemical education, equilibrium and the LeChâtelier principle: a wonderful analogy. Perhaps this analogy can be expanded upon. An equilibrium system is one that is closed; hopefully the chemical curriculum (textbook content, etc.) is not-there is a net movement to someplace else. For instance in a metabolic pathway, a classic nonequilibrium system, in which LeChâtelier arguments can (nonetheless) be used effectively,...