* TSX falls 19.05 points, or 0.16 percent, to 12,738.44 * Six of 10 main sectors decline * CN Rail drops 1.4 percent after results * Gold miners slip with bullion price By John Tilak TORONTO, July 23 (Reuters) - Canada's main stock index slipped on Tuesday after gains in energy producers and positive sentiment following China's commitment to economic reform were offset by a drop in Canadian National Railway's stock after the company's quarterly results. CN Railway shares fell 1.4 percent after the country's largest railroad posted an 11 percent rise in second-quarter adjusted profit and said its oil shipments grew. The decline came after the stock had a bit of a run-up in price before Monday's earnings report, The Toronto market hit a seven-week high earlier in the session before giving up four straight sessions of gains. Investors paid attention to Chinese Vice Premier Zhang Gaoli, who said the country, a major consumer of Canada's commodity exports, remains committed to steering its economy towards consumption as the main growth driver, and away from investment and exports, and will fine-tune policies to deal with any prolonged slowdown. Shares of energy producers climbed after the price of Brent crude rose. "Energy stocks are the feature today. There's a positive mood for the group," said John Ing, president of Maison Placements Canada. "But inventories are building, and that means the short-term price increase that we've seen will likely be temporary," he added. "Demand is still not catching up, and that will put the pressure on prices." The Toronto Stock Exchange's S&P/TSX composite index was down 19.05 points, or 0.16 percent, at 12,738.44. Six of the 10 main sectors on the index were trading lower. The materials sector, which includes mining stocks, slipped 0.3 percent, hurt by declines in shares of gold miners. Goldcorp Inc fell 0.9 percent to C$29.71. Financials, the index's most heavily weighted sector, lost 0.1 percent. Royal Bank of Canada, the country's biggest lender, was down 0.2 percent at C$64.92. CN Rail shares fell to C$103.31 and played the biggest role of any single stock in leading the market lower. Rival Canadian Pacific Railway Ltd gave back 0.5 percent to C$131.95. Those moves took the industrials sector down 0.4 percent. But energy shares were up 0.4 percent. Encana Corp rose 1 percent to C$18.21, and Suncor Energy Inc gained 0.7 percent to C$33.32.