Adjective : impalpable distinctions.    From Dictionary.com. 

This was taken off, one cup of water poured out, and three cups full of the powder, after she had ascertained its impalpability between her finger and thumb, were stirred in with a stick of cinnamon.    From Wordnik.com.  [The Mirror of Literature, Amusement, and Instruction Volume 19, No. 538, March 17, 1832] Reference

They represent metaphorically, however, certain important qualities of verse which, with the exception of rime, cannot from their very impalpability be formally explained, but can only be suggested and partially described.    From Wordnik.com.  [The Principles of English Versification] Reference

One who has faded into impalpability through death, through absence, through change of manners.    From Wordnik.com.  [Ulysses] Reference

But even out of the mouths of their soundest reasoners it is easy to demonstrate the futility, the impalpability of their axioms in general.    From Wordnik.com.  [The Works of Edgar Allan Poe — Volume 4] Reference

Perhaps one day, between them, they would break down the barrier, the strength of which seemed to lie in its very flimsiness, its impalpability.    From Wordnik.com.  [All Roads Lead to Calvary] Reference

Not often subtle in impulse or recondite in mood, his art has nothing of the impalpability, the drifting, iridescent vapours of Debussy, nothing of the impenetrable backgrounds of Brahms.    From Wordnik.com.  [Edward MacDowell] Reference

Troubles and other realities took on themselves a metaphysical impalpability, sinking to mere mental phenomena for serene contemplation, and no longer stood as pressing concretions which chafed body and soul.    From Wordnik.com.  [Tess of the d'Urbervilles] Reference

There was nothing teasing or wilfully elusive in Hawthorne's impalpability, such as I afterwards felt in Thoreau; if he was not there to your touch, it was no fault of his; it was because your touch was dull, and wanted the use of contact with such natures.    From Wordnik.com.  [Literary Friends and Acquaintance; a Personal Retrospect of American Authorship] Reference

After this, being landed, it was rapture to stroll up and down the good road, and feel it hard and real under our feet, and not an abysmal impalpability, while all the grim shapes of our dreams fled to the spectral line of small boats sustaining the ferry-barge, and swaying slowly from it as the drowned men at their keels tugged them against the tide.    From Wordnik.com.  [Italian Journeys] Reference

And, in below the sunshine of the gorse, where rough Mother Earth should have been, there lay instead a soft sunset cloud, the tender cream-yellow and green of myriads of primroses and the just uncurling fronds of the bracken -- primroses in such unbroken sheets and masses as to give a weird effect of remoteness and impalpability to that which was solid and close at hand.    From Wordnik.com.  [Pearl of Pearl Island] Reference