~Palmitic and stearic acids.~ Ordinary fats consist principally of derivatives of palmitic and stearic acids. When the fats are heated with sodium hydroxide the sodium salts of these acids are formed. If hydrochloric acid is added to a solution of the sodium salts, the free palmitic and stearic acids are precipitated. They are white solids, insoluble in water. Stearic acid is often used in making candles. ~Acids belonging to other series.~ In addition to members of the fatty-acid series, mention may be made of the following well-known acids. ~Oxalic acid~ (H_{2}C_{2}O_{4}). This is a white solid which occurs in nature in many plants, such as the sorrels. Its ammonium salt ((NH_{4})_{2}C_{2}O_{4}) is used as a reagent for the detection of calcium. When added to a solution of a calcium compound the white, insoluble calcium oxalate (CaC_{2}O_{4}) precipitates. ~Tartaric acid~ (H_{2}.C_{4}H_{4}O_{6}). This compound occurs either in a free state or in the form of its salts in many fruits. The potassium acid salt (KHC_{4}H_{4}O_{6}) occurs in the juice of grapes. When the juice ferments in the manufacture of wine, this salt, being insoluble in alcohol, separates out on the sides of the cask and in this form is known as argol. This is more or less colored by the coloring matter of the grape. When purified it forms a white solid and is sold under the name of cream of tartar. The following are also well-known salts of tartaric acid: potassium sodium tartrate (Rochelle salt) (KNaC_{4}H_{4}O_{6}), potassium antimonyl tartrate (tartar emetic) (KSbOC_{4}H_{4}O_{6}). ~Cream of tartar baking powders.~ The so-called cream of tartar baking powders consist of a mixture of cream of tartar, bicarbonate of soda, and some starch or flour. When water is added to this mixture the cream of tartar slowly acts upon the soda present liberating carbon dioxide in accordance with the following equation: KHC_{4}H_{4}O_{6} + NaHCO_{3} = KNaC_{4}H_{4}O_{6} + H_{2}O + CO_{2}. The carbon dioxide evolved escapes through the dough, thus making it light and porous. ~Citric acid~ (H_{3}.C_{6}H_{5}O_{7}). This acid occurs in many fruits, especially in lemons. It is a white solid, soluble in water, and is often used as a substitute for lemons in making lemonade. ~Lactic acid~ (H.C_{3}H_{5}O_{3}). This is a liquid which is formed in the souring of milk. ~Oleic acid~ (H.C_{18}H_{33}O_{2}). The derivatives of this acid constitute the principal part of many oils and liquid fats. The acid itself is an oily liquid. ETHEREAL SALTS When acids are brought in contact with alcohols under certain conditions a reaction takes place similar to that which takes place between acids and bases. The following equations will serve as illustrations: KOH + HNO_{3} = KNO_{3} + H_{2}O, CH_{3}OH + HNO_{3} = CH_{3}NO_{3} + H_{2}O.