Horace Gray

“ The result of these considerations is that in this act the phrase 'expressly used for manure' is equivalent to 'used expressly,' or 'particularly,' or 'especially' for manure, and denotes those substances, the only common use of which, either by themselves or in combination with other materials, is for the purpose of fertilizing the soil.
If the only common use of a substance is to be made into manure, or to be itself spread upon the land as manure, the fact that occasionally, or by way of experiment, it is used for a different purpose, will not take it out of the exemption ”

“ So, by force of the very clause in question, 'all substances expressly used for manure' must be exempt from duty, even if they are chemical products, and are scientifically classed as one kind of an article the name of which appears in Schedule A, or are spoken of in commerce by that name. The agricultural use must prevail over the scientific or commercial nomenclature. ”

“ This is manifest from the clause in the free list, immediately preceding that now in question, 'Carbon, animal, fit for fertilizing only,' as well as from the clause further on in the same list, 'Phosphates, crude or native, for fertilizing purposes.' 22 Stat. 517. Animal carbon and crude or native phosphates are both chemical products ”