Estimation of calcium in ash and forage plants and animal carcasses

One of the most abundant and important mineral constituents of nearly all agricultural products of both animal and vegetable origin is the element calcium. When such products are ignited, the entire content of calcium remains in the ash, either in the form of oxide or combined with an acid radical, such as phosphate or sulfate. An accurate method for the estimation of calcium is of prime importance in studying the relationship between the growing plant or animal on the one hand, and the soil or food supply on the other. The separation and subsequent estimation of calcium would be comparatively simple were it not for the fact that the ash of above mentioned origin invariably contains, besides calcium, other common constituents, notably phosphoric acid, whose interference during the ordinary course of analytical procedure is so well known as to require no comment. Having had occasion in the laboratory of the Iowa Agricultural Experiment Station to make a large number of calcium determinations in samples of forage crops and animal carcasses, the disadvantages and inconveniences of the existing methods soon became apparent. In the course of these analyses the method described in the subsequent pages of this paper suggested itself and, after being subjected to critical tests and comparisons with the method in common use, it was found to be superior both in regard to accuracy and convenience. Before entering upon the discussion of the proposed method for determining calcium in the presence of phosphorus, a brief survey of the literature will be given

The Separation and Gravimetric Estimation of Potassium

The market value of chloroplatinic acid, particularly under present conditions, is so high as to warrant a careful search for some cheaper reagent for the determination of potassium. Serullas, as early as 1831, proposed taking advantage of the insolubility of potassium perchlorate in concentrated alcoholic solutions and applying it as a reagent for the estimation of potassium. Unfortunately his proposal did not receive the attention it deserved because a convenient method for the preparation of perchloric acid had not at that time been worked out. Lately, Kreider elaborated a method for the preparation of perchloric acid in large enough quantities and in sufficient purity to attempt its use as a precipitant for potassium. Following the treatment suggested by Caspari he obtained very satisfactory results

Extensive dissolution of live pteropods in the Southern Ocean

The carbonate chemistry of the surface ocean is rapidly changing with ocean acidification, a result of human activities. In the upper layers of the Southern Ocean, aragonite—a metastable form of calcium carbonate with rapid dissolution kinetics—may become undersaturated by 2050 (ref. 2). Aragonite undersaturation is likely to affect aragonite-shelled organisms, which can dominate surface water communities in polar regions. Here we present analyses of specimens of the pteropod Limacina helicina antarctica that were extracted live from the Southern Ocean early in 2008. We sampled from the top 200m of the water column, where aragonite saturation levels were around 1, as upwelled deep water is mixed with surface water containing anthropogenic CO2. Comparing the shell structure with samples from aragonite-supersaturated regions elsewhere under a scanning electron microscope, we found severe levels of shell dissolution in the undersaturated region alone. According to laboratory incubations of intact samples with a range of aragonite saturation levels, eight days of incubation in aragonite saturation levels of 0.94– 1.12 produces equivalent levels of dissolution. As deep-water upwelling and CO2 absorption by surface waters is likely to increase as a result of human activities2,4, we conclude that upper ocean regions where aragonite-shelled organisms are affected by dissolution are likely to expand

Nachweis und Bestimmung der Halogensauerstoffverbindungen

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Ubiquitous molecular substrates for associative learning and activity-dependent neuronal facilitation.

Recent evidence suggests that many of the molecular cascades and substrates that contribute to learning-related forms of neuronal plasticity may be conserved across ostensibly disparate model systems. Notably, the facilitation of neuronal excitability and synaptic transmission that contribute to associative learning in Aplysia and Hermissenda, as well as associative LTP in hippocampal CA1 cells, all require (or are enhanced by) the convergence of a transient elevation in intracellular Ca2+ with transmitter binding to metabotropic cell-surface receptors. This temporal convergence of Ca2+ and G-protein-stimulated second-messenger cascades synergistically stimulates several classes of serine/threonine protein kinases, which in turn modulate receptor function or cell excitability through the phosphorylation of ion channels. We present a summary of the biophysical and molecular constituents of neuronal and synaptic facilitation in each of these three model systems. Although specific components of the underlying molecular cascades differ across these three systems, fundamental aspects of these cascades are widely conserved, leading to the conclusion that the conceptual semblance of these superficially disparate systems is far greater than is generally acknowledged. We suggest that the elucidation of mechanistic similarities between different systems will ultimately fulfill the goal of the model systems approach, that is, the description of critical and ubiquitous features of neuronal and synaptic events that contribute to memory induction