Ca
Calcium

atomic no. 20, atomic wt. 40.08, metal, row 5, col. 2A, val. 2, orbits 2-8-8-2


{Merck Index - © 1952 by Merck & Co., Inc.}

Calcium. Ca; at. wt. 40.08; at. no. 20; valence 2. Discovered in 1808 by Davy and obtained by electrolysis of calcium chloride.

Lustrous, silver-white surface when freshly cut, but gradually becomes gray due to coating of oxide. It is available in commerce in the form of gray, hard lumps or turnings. Usually contains about 0.5% impurities. d. 1.55. m. 810°. Sublimes below its melting point in vacuum. b. 1170°. Readily decomposes water with evolution of hydrogen; slowly decomposes alcohol.

Keep dry and well closed.

Use: As deoxidizer in metallurgy for preparing alloys of difficulty alloyable metals; as a "getter" in electronic vacuum tubes.

Commercially available.

{Mineral Deficiencies in Plants}

Calcium occurs in plants chiefly in the leaves and the amounts present in seeds and fruits are relatively low.

One of its main functions is as a constituent of the cell wall, the middle lamella of which consists largely of calcium pectate. This function appears to be of fundamental importance since, if calcium is replaced by any other of the essential elements, such as magnesium or potassium the organic materials and mineral salts in the cells are readily leached through the cell walls.

Other functions attributed to calcium are as follows:

It provides a base for the neutralization of organic acids; it is concerned with activities of growing points (meristems), especially with root tips: it may be of importance in nitrogen absorption.

Although a large proportion of the calcium contained in the plant may be soluble in water-as much as 60% in cabbage-calcium does not appear to move freely from the older to the younger parts of plants and hence young tissues contain lower proportions of calcium than older ones. This may explain why calcium deficiency effects begin at the tips of shoots.

 
Link to Chemical Elements.com


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