For the wet ashing method before chemical analysis of preservative wood, the perchloric acid digestion method is specified in the industry standard as follows:

1、試劑，⑴濃硝酸（70%，AR）;⑵濃硫酸;（98%，AR）(3)濃高氯酸（70%，AR）;（4）酸氧化劑。加185毫升的濃高氯酸到100毫升的蒸餾水中，然后慢慢慢地加入270毫升地濃硫酸，并攪拌混合均勻。

1. Reagent, ⑴ concentrated nitric acid (70%, AR); (2) concentrated sulfuric acid; (98%, AR) (3) concentrated perchloric acid (70%, AR); (4) Acid oxidant. Add 185 ml of concentrated perchloric acid to 100 ml of distilled water, then slowly add 270 ml of concentrated sulfuric acid, stir and mix evenly.

2、操作過程。將木材式樣在烘箱中125℃干燥約2.5小時至恒重，用靈敏度為0.1毫克地分析天平準確稱取多不超過5克地木粉試樣，放置在500毫升地凱氏燒瓶中，加入3～5個玻璃珠，沿瓶壁慢慢加入30毫升地硫酸，使木粉潤濕，低溫在抽氣狀態下慢慢消化（100℃）,抽氣調節在燒瓶口處棕色煙為準。

2. Operation process. Dry the wood sample in the oven at 125 ℃ for about 2.5 hours to constant weight, accurately weigh the sample of no more than 5 grams of wood powder with an analytical balance with a sensitivity of 0.1 mg, place it in a 500 ml Di Kjeldahl flask, add 3 ~ 5 glass beads, slowly add 30 ml of sulfuric acid along the bottle wall to wet the wood powder, and slowly digest it at low temperature under air extraction (100 ℃), The exhaust adjustment shall be subject to brown smoke at the bottle mouth.

約20分鐘后，棕色煙消失，木材已完全消化、溶解。如果還沒有消化完全，則再加入10毫升硝酸，繼續消化。通常需要超過30毫升的硝酸用量，但應避免過量。

After about 20 minutes, the brown smoke disappeared and the wood was completely digested and dissolved. If the digestion is not complete, add 10 ml of nitric acid and continue the digestion. More than 30 ml of nitric acid is usually required, but excess should be avoided.

用滴管或注射器，從燒瓶接頭入口處向瓶內滴加10毫升酸氧化劑。約40分鐘后，可以看到白色濃煙，溶液呈綠色。溶液若轉變成黑色，則使其冷卻，再加入10毫升硝酸，慢慢加熱，直到溶液轉為綠色。如果試樣中沒有鉻，那么消化就此完成。如果試樣中存在鉻，則繼續加熱，直到溶液變橙色，立即停止加熱，將燒瓶撤出加熱器，消化過程即告訴完成。待消化液冷卻至室溫，并按正常程序稀釋后，即可做各種成分分析。

Using a dropper or syringe, drop 10 ml of acid oxidant into the flask from the inlet of the flask connector. After about 40 minutes, you can see white smoke and the solution is green. If the solution turns black, cool it, add 10 ml nitric acid and heat it slowly until the solution turns green. If there is no chromium in the sample, the digestion is completed. If there is chromium in the sample, continue heating until the solution turns orange, stop heating immediately, withdraw the flask from the heater, and the digestion process is completed. After the digestive solution is cooled to room temperature and diluted according to normal procedures, various components can be analyzed.

砷、銅和磷酸鹽分析。用容量瓶和合適器皿稀釋消化液，再測定砷或銅時不要用不經稀釋的消解液，液不允許將消液加熱煮得太干，以免發生爆炸。

Arsenic, copper and phosphate analysis. Dilute the digestion solution with volumetric flask and appropriate utensils. Do not use undiluted digestion solution when determining arsenic or copper. It is not allowed to heat and boil the digestion solution too dry to avoid explosion.

3、特別安全防范措施。應用本方法注意，如果使用高氯酸方法不當或不小心，會引起劇烈且危險的爆炸。一下兩點試消解木材時必須防范的：

3. Special safety precautions. Note that if perchloric acid is used improperly or carelessly, it will cause violent and dangerous explosion. The following two points must be prevented when trying to digest wood:

（1）試樣和硝酸混合后，在棕色煙霧沒有停止逸出以前，嚴禁再加如試劑；

(1) After the sample is mixed with nitric acid, it is strictly prohibited to add reagent before the brown smoke stops escaping;

（2）高氯酸應和硫酸混合成為酸性氧化劑后再加入到消化混合物中。一旦消化開始，應避免添加木材，或與其他有機物質接觸。如果不小心發生這樣的接觸，應立即將大量冷水加入到消化瓶中以制止反應的進一步發生。

(2) Perchloric acid shall be mixed with sulfuric acid to form an acidic oxidant and then added to the digestion mixture. Once digestion begins, avoid adding wood or contact with other organic substances. If such contact occurs accidentally, a large amount of cold water should be added to the digestion bottle immediately to prevent further reaction.