OBS. 4.—­The sense and relation of words in sentences, as well as their particular form and meaning, must be considered in parsing, before the learner can say, with certainty, to what class they belong.  Other parts of speech, and especially nouns and participles, by a change in their construction, may become adjectives.  Thus, to denote the material of which a thing is formed, we very commonly make the name of the substantive an adjective to that of the thing:  as, A gold chain, a silver spoon, a glass pitcher, a tin basin, an oak plank, a basswood slab, a whalebone rod.  This construction is in general correct, whenever the former word may be predicated of the latter; as, “The chain is gold.”—­“The spoon is silver.”  But we do not write gold beater for goldbeater, or silver smith for silversmith; because the beater is not gold, nor is the smith silver.  This principle, however, is not universally observed; for we write snowball, whitewash, and many similar compounds, though the ball is snow and the wash is white; and linseed oil, or Newark cider, may be a good phrase, though the former word cannot well be predicated of the latter.  So in the following examples:  “Let these conversation tones be the foundation of public pronunciation.”—­Blair’s Rhet., p. 334.  “A muslin flounce, made very full, would give a very agreeable flirtation air.”—­POPE:  Priestley’s Gram., p. 79.

   “Come, calm Content, serene and sweet,
    O gently guide my pilgrim feet
    To find thy hermit cell.”—­Barbauld.

OBS. 5.—­Murray says, “Various nouns placed before other nouns assume the nature of adjectives:  as, sea fish, wine vessel, corn field, meadow ground, &c.”—­Octavo Gram., p. 48.  This is, certainly, very lame instruction.  If there is not palpable error in all his examples, the propriety of them all is at least questionable; and, to adopt and follow out their principle, would be, to tear apart some thousands of our most familiar compounds. “Meadow ground” may perhaps be a correct phrase, since the ground is meadow; it seems therefore preferable to the compound word meadow-ground.  What he meant by “wine vessel” is doubtful:  that is, whether a ship or a cask, a flagon or a decanter.  If we turn to our dictionaries, Webster has sea-fish and wine-cask with a hyphen, and cornfield without; while Johnson and others have corn-field with a hyphen, and seafish without.  According to the rules for the figure of words, we ought to write them seafish, winecask, cornfield.  What then becomes of the thousands of “adjectives” embraced in the “&c.” quoted above?