Are you talking about a preserved lung in a cadaver? In that case the visceral pleura cannot be separated from the lung parenchyma. If you touch or scrape a lung out of your cadaver you are dealing with the visceral pleura covering the surface of the lung. I haven't dealt with a living or unpreserved lung, but I believe in that case it is easier to separate the visceral pleura. The parietal pleura is different. That is the pleura which lines the inside of the thoracic cavity, but does not directly touch the lung.