Columbia Encyclopedia

(Encyclopedia) asthma ăzˈmə, ăsˈ– [key], chronic inflammatory respiratory disease characterized by periodic attacks of wheezing, shortness of breath, and a tight feeling in the chest. A cough producing sticky...

(Encyclopedia) membrane, structure composed mostly of lipid and protein that forms the external boundary of cells and of major structures within cells. Membrane organization is based on a sheet two molecules thick�...

(Encyclopedia) silica or silicon dioxide, chemical compound, SiO2. It is insoluble in water, slightly soluble in alkalies, and soluble in dilute hydrofluoric acid. Pure silica is colorless to white. It occurs in sev...

(Encyclopedia) snowball earth, hypothesized condition in which the earth was covered completely by ice during several periods in the Proterozoic. The hypothesis was originally developed to explain evidence of the co...

(Encyclopedia) gas, in physics, one of the three commonly recognized states of matter, the other two being solid and liquid. A substance in the gaseous state has neither definite shape nor definite volume. Like liqu...

(Encyclopedia) enzyme, biological catalyst. The term enzyme comes from zymosis, the Greek word for fermentation, a process accomplished by yeast cells and long known to the brewing industry, which occupied the atten...

(Encyclopedia) volcano, vents or fissures in the earth's crust through which gases, molten rock, or lava, and solid fragments are discharged. Their study is called volcanology. The term volcano is commonly applied b...

(Encyclopedia) niobium nīōˈbēəm [key], metallic chemical element; symbol Nb; at. no. 41; at. wt. 92.90638; m.p. about 2,468℃; b.p. 4,742℃; sp. gr. 8.57 at 20℃; valence +2, +3, +4, or +5. Niobium is a rare...

(Encyclopedia) bismuth bĭzˈməth [key] [Ger. Weisse Masse=white mass], metallic chemical element; symbol Bi; at. no. 83; at. wt. 208.98040; m.p. 271.3℃; b.p. about 1,560℃; sp. gr. 9.75 at 20℃; valence +3 or ...

(Encyclopedia) indium ĭnˈdēəm [key], a metallic chemical element; symbol In; at. no. 49; at. wt. 114.818; m.p. 156.6℃; b.p. about 2,080℃; sp. gr. 7.31 at 20℃; valence +1, +2, or +3. Indium is a soft, malle...