This section is from the book "The London Art Of Cookery and Domestic Housekeepers' Complete Assistant", by John Farley. Also available from Amazon: The London Art of Cookery.
In buying of butter, you must not trust to the taste the seller gives you, lest he give you a taste of one lump, end sell you another. In choosing salt butter, trust rather to your smell than taste, by putting a knife into it, and applying it to your nose. If the butter be in a cask, have it unhooped, and thrust in your knife, between the staves, into the middle of it; for the top of the cask is sometimes better butter than the middle, owing to artful package.
 
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