United States. War Department

“ Prepositions which end in a mute present a special case, because Russian prepositions are spoken as if they were part of the following word. A preposition which ends in a unvoiced mute follows the general rule: the mute is voiced before voiced mutes other than [v] : от отца [at atca] "from the father," от сына [at sina] "from the son," от врага [ad vraga] "from the enemy," but от брата [ad brata] "from the brother," от дочери [ad doč'rji] "from the daughter." ”

“ The remaining consonants [l, m, n, r, y,] are non-mutes.
Final Mutes. At the end of a Russian word, as it is spoken alone, only unvoiced mutes occur. When an unvoiced mute comes to be at the end of a word, it is unchanged: пилоты [pjiloti] "pilots," пилот [pjilot] "pilot"; мосты [masti] "bridges," мост [most] "bridge"; души [duči] "shower baths," душ [duš] "shower bath." But when a voiced mute comes to be at the end of a word, it is replaced by the corresponding unvoiced mute. ”

“ The sound [č] before [n] is often replaced by [š] : скучать [skučatj] "to be bored," but скучно [skusna] "tiresome." In less common words the [č] is often kept. In the dictionary we indicate the change in the words where it is most commonly made: скучно [-šn-] .
Weakening of Vowels. In unstressed syllables, vowels are weakened, shortened, and slurred. In all unstressed syllables the distinction between [a] and [o] is lost. The weakening of unstressed vowels is not shown in the spelling, except for a few instances. ”