The owners of watches sometimes subject them to very hard treatment by using perfumes, etc., and then some people perspire more than others, while the perspiration of some persons contains more acids, or is more rancid, than that of others. For these reasons the method of testing oil by putting it on watches kept to loan to customers as Saunier recommends cannot be relied on. Oils should be kept in a clean, cool, dark place. The wrapper or label on the bottle should be dark blue or black, to exclude all light, as, if this is not done, the oil will be more liable to decomposition, except in the case of a mineral oil, which is not affected by light. All vegetable and animal oil which has been "bleached" by exposure to the light is more liable to decomposition on exposure to air than that which is unbleached. ~88. The Effect of Age on Oils.~ Writing on this subject Mr. Henry G. Abbott[28] states as follows: "There is a popular fallacy existing in the trade that oils should be used when fresh, and even that acknowledged authority, Saunier, says, 'do not buy from motives of economy bottles that have laid for years in the shop.' This may be true and probably is in regard to animal and vegetable oils, which are likely to become rancid if kept for a long time, but William F. Nye, one of the largest and most celebrated manufacturers of fine watch and chronometer oils in the world, declares that blackfish oils are improved by age, and his oils are seldom placed on the market in the same year as obtained. We are indebted to the same authority for the statement that oils of this kind are clearer and more brilliant after some years than fresh oils." Though Mr. Abbott has made some very valuable additions to the literature of the profession, the author begs permission to call attention, in reference to this, to the following facts: Mr. Abbott says that vegetable and _animal_ oils are likely to become rancid if kept for a long time, but _blackfish_ oils are not. Brant[29] states that the porpoise or _Phocoena communis_, Cuv., and the blackfish, or _Phocoena globiceps_, are of the subdivision _Delphinodea_, or dolphins, of the family of _Cetacea_, or whales, an order of the vertebrated mammiferous marine _animals_. Adler Wright[30] states that "the term 'train oil,' strictly speaking, applies to any oil extracted from the blubber of cetaceans and the allied marine mammalia, such as the seal, porpoise, dolphin and walrus." Huxley classes among cetacea the dolphins, porpoises, grampus and narwhal. Authorities might be quoted _ad infinitum_ to show, not only that porpoise-jaw oil and blackfish-melon oil _are animal oils_, but that they possess properties similar to other animal oils as far as their liability to decompose by age, more or less, is concerned.